Oh, and you'll want to get MusicMatch (the registered version). You can have it convert every single music file into a low-bitrate (like 112 or 96) mp3 file effortlessly (just choose your music folder, choose the output folder if you don't want it to overwrite, and then wait for it to be done), so you can fit as many songs on your player as you could imagine. Lowering the bitrate of your files makes a huge difference.
I'm a bit fussy with my MP3s, I'm willing to trade off file size for audio quality. I use a freeware program called CD-ex to convert which is really easy to use, basically almost drop and drag. The alt.preset.standard setting on LAME, which is CD-ex's MP3 encoder, gives you a variable bit rate between 128 and 192, usually a lot closer to 128 so the files aren't that much bigger. The thing is, I've only done a little bit with WMA files, but I encoded one album of those at a very low bit rate, like in the 80s, and was impressed with the sound. I'd heard that it does better than MP3 at low bit rates, I just haven't messed with it that much because I figure that MP3 is still the standard and will remain that way for a while, even the iPod plays MP3s.