you aren't stuck buying more tracks after your computers die. You are only allowed 5 authorized computers at a time, but you can deauthorize computers and reautorize others. If you are in iTunes go to the store menu and if gives you both options to authorize or deauthorize the computer. You can also from a different computer deauthorize an entire account under the advanced menu if all your 5 computer blow up at the same time and then start reauthorizing new computers.
However all this authorizing deauthorizing talk is irrelevant if you strip the DRM from your music that you buy from the iTunes store. Just download QTfairuse from this
link. It is updated within days from the time that Apple updates their DRM. It is so easy to run. When you launch the application it sorts through your entire library and finds any DRM music and displays it to you. Then you just click a button and it starts stripping the DRM song after song and it saves a copy of your DRM version in a seperate folder. Then it redirects your library file to look at the newly DRM stripped files instead of the old DRM ones. Your playlists and everything stay the same. An important note is that it strips the DRM from the music but not your iTunes account information so I wouldn't recommend sharing the music after it is stripped.
If you want to play your AAC music in WMP download this
plugin. It is right at the top of the page where it says "GET IT HERE". Unfortunatley WMP will not let you sync aac files to your WM device even though you can listen to them and make playlists of them in WMP with this plugin.
you can even sync your playlists from iTunes to WMP or WMP to iTunes with musicbridge explained
here.
I made another thread that explains how I sync iTunes playlists and podcasts to my Axim
here.
In the end if you are concerned about playback and degrading quality from lower bitrates then you should just buy the CD and rip it at high qualities and you are free to do what ever you please with it after that.