My old Dell running Windows XP completely crashed so I got an iMac. I haven't plugged my iPod touch in yet, since I don't know what will happen and I really can't afford to replace all of the music on it. Any suggestions would be greatly appreciated.

It won't be a problem if you use AVCWare iPod to iPod/Computer/iTunes Transfer.
It automatically transfers your iPod and iPhone music, video, playlist, photos to computer and iTunes. Backup all your music and video in a couple of clicks. Really makes music and videos sharing pretty simple and enjoyable. Wish this can help and good luck.

I think its step by step guide is most helpful.
http://iphone-to-computer.net/transfer-songs-videos-photos-playlists-from-ipod-to-computer-itunes.html

It is easy to use and you can try it now.
http://www.google.com/search?hl=en&newwindow=1&q=site%3Aiphone-to-computer.net++avcware+ipod+transfer&btnG=Search&aq=f&oq=&aqi=

I don't know much about MAC, but what you can do is go to the Itune settings and disable the auto sync. That way you plug your IPod without sync. Now, purchase Monkey Media and install it in your MAC, sync Monkey Media with your IPod, this will transfer all your music from your IPod to Monkey Media library. It also should be saved in My Music folder, well, at least in a PC.
Now open ITunes, click File, add media to library and that's it. Now sync your IPod with ITune. It will still say that it will erase everything in your IPod, but it should be already in ITune's library.

Don't auto sync because ipod can only sync with one computer itunes or the ipod files will be erased.
itunes blocks this function since itunes is the tool with one way to transfer files from itune to ipod. you must utilize other tools to achieve that. There're couple of tools for transferring the files between ipod and computer (for backup)depends on your demands, e.g transfer only songs/videos, transfer photos etc. You can have a look of below review site, hope it useful.

Don't auto sync because ipod can only sync with one computer itunes or the ipod files will be erased.
itunes blocks this function since itunes is the tool with one way to transfer files from itune to ipod. you must utilize other tools to achieve that. There're couple of tools for transferring the files between ipod and computer (for backup)depends on your demands, e.g transfer only songs/videos, transfer photos etc. You can have a look of below review site, hope it useful.

All you need is to get all existing music/videos from your iPod back to your computer and iTunes. Simply use this handy transfer program called Tansee iPod Transfer
http://www.gutensoft.com/Utilities/Tansee-iPod-Transfer.htm
Many of my friends are using it for its easy and safe transfer.

With just a few simple clicks, it will help you copy all videos/songs from iPod back to your selected folder on your computer, and then you can easily add those files back to iTunes.
More importantly, this won't overwrite any original files on your iPod. And all song names are preserved.

In this case, all songs/videos (both new and old) are on your iTunes library that you can syn with whenever you wish to without deleting any files.
Here is step-by-step guide on the whole process:
http://gutensoft.com/Guide/How-to-transfer-songs-and-videos-from-ipod-to-computer.htm

Best luck!
For more iPod support information you can also go to http://www.apple.com

You can use an ipod to Mac transfer program to help.I personally use AVCWare Mac iPod to iPod/Computer/iTunes Transfer.It helps me to copy my songs/videos/photos/playlists etc from ipod to Mac directly and safely.It works well for me,you can give it a try.
real purchase it at: http://www.dvd-video-soft.com/macconverter/mac-ipod-to-ipod-computer-itunes-transfer.html

Hope it helps.
You can keep asking on http://answers.yahoo.com or use http://www.ask.com to search more