I actually, I misspoke - i meant "can you paste the HTML you were trying to use into the forums" so i could see it...but no matter.
Yeah, I got that same issue when trying to recreate your bug. I tried adding a form to a generic control, and adding a submit button. I ended up having to log out, log back in and delete the control. Sitefinity has problems with that multiple form tag.
I use Visual Studio 2008, but i think Sitefinity will also work with Visual Studio Express (which is free: Download
*select web developer version). If this is incorrect someone please interject. Anyway, if you need this kind of functionality, I think the best answer is to create a user control (.ascx) and upload that into sitefinity. If you had someone write this into a .aspx, they could rewrite it as a user control which you can upload to the site.
Is that a possibility?