As far as I know, music purchased at the iTunes Music Store is protected with DRM called "FairPlay" that only Apple's iPods can use.
You could always burn your purchased iTunes store music to a music CD and rerip it back to your computer, but I guess there's some quality loss with that, plus you have to reenter the songs name, artist, etc.
There is also another newly released program that's supposed to remove Apple's DRM, but I haven't played with it myself.
After having had a few Creative products over the years, I happily switched to the iPod. (Granted this was a few years ago, ... don't know how good the Creative stuff has become since, but I'm perfectly happy with my iPod!)
If I were interested in getting a new toy, I would get a Nintendo DS Lite. They really are a lot of fun.
I just don't understand why you would need another music player, unless you are unhappy with the iPod. I would get something that is made for a different use, like playing games. But that is just my 2 cents.