Here's how you do it.
1. Hook the iPod up to the computer. If iTunes pops up and asks you if you want to replace anything, say no. You can hit ctrl-shift-esc and go to processes, then close the iPodService.exe to get you more time.
2. Go to My Computer. It should list the iPod as whatever you named the iPod (like Joe's iPod). Click on the drive.
3. You should see some folders. If you don't see one named iPod_Control, go to the Tools option at the top of the window (its on the bar with File and Edit). Click on the "Folder Options" selection at the bottom. When that opens, click the View tab at the top, then scroll down the list and choose the "show hidden files and folders" button under the Hidden Files and Folders folder. The iPod_Control should show up. If not, go to the address bar and type it in.
4. Under iPod_Control, you should see a Music folder. From here, you can either copy the whole folder and paste it somewhere on the computer and put them in iTunes later, or you can find songs. If you do a search, you should be able to find songs by putting in what to search full under "word or phrase in file".
If you want to put in music that will play in the iPod directly, you're going to have to go into one of the folders in the music folder (usually like f00 or f01 or something), find a file (usually with a random 4 letter name like MLKJ), take the song you want to play, rename it as the song you're replacing, then copy and paste it in there.
Usually you want to reaname the song you're replacing first, then find it later. If you want to make sure you don't replace something you want, view the folder with details, right-click the top of the window in the bar that says "name" and check Author or Title. This will show what you're replacing.
5. If you want to put music on the iPod but don't want to have to lose anything, your best bet is to take the songs you want, put them in a folder on the iPod, and take them back to your home computer, add them to iTunes, then put them on your iPod.
6. To add songs to iTunes from a folder, go to File, click Add Folder, then find the folder you want and go. It automatically keeps the names and usually the album art with the songs.