It's actually pretty easy, and you can even find a certain album,song, or artist and take only that to your computer from your ipod.
You do not need to download any extra programs or software. When you download a lot of programs to your computer it tends to slow things down after a while, so getting new software for each task is not a good idea. Use the tools you already have:
PC running XP or Vista
these are all you need.
note: if you do something crazy and mess up your ipod or something, don't blame me. Ipod hacks are not for the faint of heart. (although this is not any kind of "hack", considering it uses only the programs meant to be used with an ipod. perhaps you should send a note to steve jobs about that, huh?) But if you're willing to take the risk this is an easy way to get that one album back to your itunes.
Step 1: Prep your ipod/itunes
Eject your ipod and close itunes, then start over by plugging you ipod back in.