You can't do it using the html content feature, only a link will work there, paypal can also generate a link suitable for email and you could use that, but to use the form elements you would need to create a custom feature PayPalButton.ascx file with the following code:
<%@ Control Language="C#" ClassName="PayPalBuyNow.ascx" Inherits="mojoPortal.Web.SiteModuleControl" %>
<%@ Import Namespace="mojoPortal.Business" %>
<%@ Import Namespace="mojoPortal.Business.WebHelpers" %>
<%@ Import Namespace="mojoPortal.Web.Framework" %>
<%@ Import Namespace="mojoPortal.Web.Controls" %>
<%@ Import Namespace="mojoPortal.Web.Editor" %>
<%@ Import Namespace="mojoPortal.Net" %>
<script runat="server">
// Author: Joe Audette
// Created: 2010-12-14
// Last Modified: 2010-12-14
protected string HostedButtonId = "XXXXXXXXXX"; // your PalPal Generated value for hosted_button_id
private string buttonImageUrl = "https://www.paypal.com/en_US/i/btn/btn_buynowCC_LG.gif"; // or donate button https://www.paypal.com/en_US/i/btn/btn_donateCC_LG.gif
private string payPalPostUrl = "https://www.paypal.com/cgi-bin/webscr"; // you shouldn't need to change this
protected void Page_Load(object sender, EventArgs e)
{
LoadSettings();
}
private void LoadSettings()
{
Title1.Visible = !this.RenderInWebPartMode;
if (this.ModuleConfiguration != null)
{
this.Title = this.ModuleConfiguration.ModuleTitle;
this.Description = this.ModuleConfiguration.FeatureName;
}
btnPayPal.ImageUrl = buttonImageUrl;
btnPayPal.PostBackUrl = payPalPostUrl;
}
</script>
<portal:OuterWrapperPanel ID="pnlOuterWrap" runat="server">
<mp:CornerRounderTop id="ctop1" runat="server" EnableViewState="false" />
<portal:InnerWrapperPanel ID="pnlInnerWrap" runat="server" CssClass="panelwrapper papalmodule">
<portal:ModuleTitleControl id="Title1" runat="server" EnableViewState="false" />
<portal:OuterBodyPanel ID="pnlOuterBody" runat="server">
<portal:mojoRating runat="server" ID="Rating" Enabled="false" />
<portal:InnerBodyPanel ID="pnlContent" runat="server" CssClass="modulecontent">
<p>You can hard code the html description here.</p>
<input type="hidden" name="cmd" value="_s-xclick">
<input type="hidden" name="hosted_button_id" value='<%= HostedButtonId %>'>
<input type="hidden" name="encrypted" value="-----BEGIN PKCS7-----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-----END PKCS7-----
">
<asp:ImageButton id="btnPayPal" runat="server" />
<img alt="" border="0" src="https://www.paypal.com/en_US/i/scr/pixel.gif" width="1" height="1">
</portal:InnerBodyPanel>
<portal:EmptyPanel id="divFooter" runat="server" CssClass="modulefooter" SkinID="modulefooter"></portal:EmptyPanel>
</portal:OuterBodyPanel>
<portal:EmptyPanel id="divCleared" runat="server" CssClass="cleared" SkinID="cleared"></portal:EmptyPanel>
</portal:InnerWrapperPanel>
<mp:CornerRounderBottom id="cbottom1" runat="server" EnableViewState="false" />
</portal:OuterWrapperPanel>
And you would then install it in your site as described in the Hello World article.
Hope that helps,
Joe