Using iPod Library

Ok, so I have an iPod. I have a computer at home that I used to have internet access on, so of course all of my music is on that computer. Now that I can't afford the net and I use the computers at my Uni campus I want to know how I can download music from the iTunes store and on to my iPod without erasing my Library on my iPod. I have looked through all of the instructions and FAQ's and I can't seem to find the info I am looking for.

Basically the question is, how do I use my iPod on two separate computers, keep my current song list/library and add to it from the school computer?

Ummm I don't think that is the answer to the question I have.

Ok, here's another go at what I want to do . . . I have my entire library on my iPod, that is what I want. But I take my iPod to school with me, hook it up to one of the Apple computers on campus and my library does come up when I iPod has hooked up and iTunes is running. How do I transfer the library/song list on my iPod (or on my home computer) to the Apple computer at school?
I have tried downloading the free songs before from school to iTunes and then transfer it to my iPod but when I did that it downloaded the ONE SONG and deleted my entire library of 400 songs that were already on my iPod. I then had to go home and put my library on my iPod which means the one downloaded song was then lost . . . I want to know how can I use both computers, download music to iTunes at school and the on to my iPod withouth losing my current song list.

If you want to transfer your songs from your ipod to your computer at school you will have to buy a special program for it.

I don't know whats its called but Best Buy should carry these programs.