Edit in JSFiddle

dojo.require("dojo.parser");
dojo.require("dijit.Dialog");
dojo.require("dijit.form.Form");
dojo.require("dijit.form.ValidationTextBox");
dojo.require("dijit.form.CheckBox");
dojo.require("dijit.form.RadioButton");
dojo.require("dijit.form.Select");
dojo.require("dijit.form.Button");
dojo.require("dojox.form.PasswordValidator");
dojo.require("dojox.form.manager._Mixin");
dojo.require("dojox.form.manager._NodeMixin");
dojo.require("dojox.form.manager._EnableMixin");
dojo.require("dojox.form.manager._ValueMixin");
dojo.require("dojox.form.manager._DisplayMixin");
/* Disabled for JSFiddle. dojo.requireLocalization("my", "SignupForm"); */

dojo.ready(function() {
    function submitForm(data) {
        var dfd = new dojo.Deferred();
        console.log("Submitting data", data);
        setTimeout(dojo.hitch(dfd, "resolve"), 2000);
        return dfd.promise;
    }
    
    var i18n = /* Disabled for JSFiddle. dojo.i18n.getLocalization("my", "SignupForm"); */ {
        username: "Username",
        usernameRules: "Username must be letters and numbers only, and at least 4 characters long",
        password: "Password",
        verifyPassword: "Verify password",
        agreeTerms: "I agree to the T&Cs",
        newsletter: "Newsletter?",
        yes: "Yes",
        no: "No",
        frequency: "Frequency",
        daily: "Daily",
        weekly: "Weekly",
        monthly: "Monthly",
        signUp: "Sign up",
        pleaseWait: "Please wait…",
        success: "It worked! Yay!",
        ok: "OK!"
    };

    dojo.declare("my.SignupForm", [dijit.form.Form,
                                   dojox.form.manager._Mixin,
                                   dojox.form.manager._NodeMixin,
                                   dojox.form.manager._EnableMixin,
                                   dojox.form.manager._ValueMixin,
                                   dojox.form.manager._DisplayMixin], {

        templateString: dojo.byId("SignupFormTemplate").innerHTML,
                                       
        i18n: i18n,
        
        postCreate: function(){
            this.watch("state", this.checkValid);
            this.inherited(arguments);
        },
                                       
        startup: function(){
            if(this.dialog){
                new dijit.form.Button({
                    type: "button",
                    label: this.i18n.ok,
                    onClick: dojo.hitch(this, function(){
                        this.dialog.hide();
                    })
                }).placeAt(this.successNode);
            }
            this.inherited(arguments);
        },
        
        checkValid: function(){
            this.enable({ submitForm: this.isValid() && this.elementValue("agree") });
        },
        
        checkNewsletter: function(value){
            this.show({ newsletterFrequency: value === "1" });
            this.dialog && this.dialog.layout();
        },

        onSubmit: function(evt) {
            evt.preventDefault();

            submitForm(this.get("value")).then(dojo.hitch(this, function(data) {
                this.show({
                    spinnerNode: false,
                    successNode: true
                });
                this.dialog && this.dialog.layout();
            }), dojo.hitch(this, function(err) {
                this.show({
                    spinnerNode: false,
                    formNode: true
                });
                this.dialog && this.dialog.layout();
            }));

            this.show({
                spinnerNode: true,
                formNode: false
            });
            this.dialog && this.dialog.layout();
        }
    });

    app = {
        dialog: new dijit.Dialog().placeAt(document.body),
        showSignupForm: function() {
            this.dialog.set({
                title: i18n.signUp,
                content: new my.SignupForm({
                    dialog: this.dialog
                })
            });
            this.dialog.show();
        }
    };

    dojo.parser.parse();
});

<script id="SignupFormTemplate" type="text/html">
    <form dojoAttachPoint="containerNode" dojoAttachEvent="onreset:_onReset,onsubmit:_onSubmit" ${!nameAttrSetting}>
        <div dojoAttachPoint="formNode">
            <div>${i18n.username}: <input dojoType="dijit.form.ValidationTextBox" name="username" required regExp="^[A-Za-z0-9]{4,}$" promptMessage="${i18n.usernameRules}"></div>
            
            <div dojoType="dojox.form.PasswordValidator" name="password">
                <div>${i18n.password}: <input type="password" pwType="new"></div>
                <div>${i18n.verifyPassword}: <input type="password" pwType="verify"></div>
            </div>
            
            <div><label><input dojoType="dijit.form.CheckBox" name="agree" observer="checkValid"> ${i18n.agreeTerms}</label></div>
            
            <fieldset>
                <legend>${i18n.newsletter}</legend>
                
                <label class="i"><input dojoType="dijit.form.RadioButton" name="newsletter" value="1" observer="checkNewsletter"> ${i18n.yes}</label>
                <label class="i"><input dojoType="dijit.form.RadioButton" name="newsletter" value="0" checked observer="checkNewsletter"> ${i18n.no}</label>
                
                <div dojoAttachPoint="newsletterFrequency" style="display:none">
                    ${i18n.frequency}:
                    <select dojoType="dijit.form.Select" name="frequency">
                        <option value="daily">${i18n.daily}</option>
                        <option value="weekly">${i18n.weekly}</option>
                        <option value="monthly">${i18n.monthly}</option>
                    </select>
                </div>
            </fieldset>
            
            <input dojoType="dijit.form.Button" name="submitForm" type="submit" label="${i18n.signUp}" disabled>
        </div>
        <div dojoAttachPoint="spinnerNode" style="display:none">${i18n.pleaseWait}</div>
        <div dojoAttachPoint="successNode" style="display:none">${i18n.success}</div>
    </form>
</script>

<input dojoType="dijit.form.Button" type="button" label="Sign up now" onclick="app.showSignupForm()">