Flash memory at those sizes is stupidly expensive. Why not get an iPod (available for Windows) with a 5, 10, or 20 gig hard drive? I have the original, and I love it. Nice sound quality, 1200 songs, never skips, great software...
There are alternatives out there, of course. However, most of the competing products are a lot bigger. Needless to say, none are as slick. I may be a Mac nut, but I genuinely think this is the best MP3 player out there...
http://www.apple.com/ipod/