I'd recommend you look at some of the numerous aspx pages that are delivered with mojoPortal. There are a lot of them under /Admin. So you'll place the aspx page wherever you want it linked (the web root is one option, which would give you a link of www.mysite.com/mypage.aspx). Your mypage.aspx.cs code will get compiled into a DLL if you're using the code behind method (as the delivered mojoPortal code does). That DLL goes into the /bin folder. So basically it's very similar to developing a custom mojoPortal module, except that you are creating a real standalone page instead of a feature that can be placed on any page within the context of the mojoPortal site's virtual structure.
Don't rely on the wrapper that Joe provided in that old forum post. Most likely it has changed, and the Codesmith templates or an existing aspx page will be the best way to model your new page.
Jamie