This site is NO LONGER being maintained for the "ALL NEW" site that talks about the new iMovie 11 please visit TheUnofficialiMovieFAQ.com
Is there a Windows based version of iMovie for Windows?
In a word. NO. There is nothing that compares to iMovie currently available for Windows.
How about close to iMovie?
Not really... but one of my favorite and "cheap" video editors for Windows was the Ulead Video Studio. While more than the cost of iLife it does a decent job of making movies and DVD's.
If you are in the market for a new computer and not ready to make the leap to a Mac then you may want to consider a Intel based Macintosh. They can boot both Windows and OS X. Then you could run Windows till you make the transition to all Mac based programs.