Yes.. this is no problem. The only two tricky things, as listed by other posters, is making one grub setup that contains the configuation for both.

The only other issue is UID numbers, and which versions of gnome/kde they use.. (sometimes in-compatable config files)

On an advocasy note.. grab Ubuntu, it's excelent.
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80gig red mk2 -- 080000125
(No, I don't actually hate Alan Cox)