Lost 1st iPod Nano, got 2nd for wife w/ songs already on it. Help!

I originally has a iPod Nano & I had been using iTunes and had a nice accumulation of songs, but lost the iPod. Got a Nano for wife off eBay that already has songs on it. She wants MOST of these songs off, and would add a few I have in my iTunes before starting her own collection. What do I do so that the computer will recognize this new iPod, & forget the lost one? How do I erase most of the songs on the ebay iPod and add a few I had on my iTunes that she likes?? Once we know that...what to do if I get a replacement iPod from Santa? How will that factor in?
This is my first day on this forum & my first post....so thanks in advance for your help.

I don't think you can just delete some of the songs. You will have to reformat it completely to add songs from your itunes library. I'm suprised the guy you bought it off of didn't reformat it before selling it to you.

Or you could use a program like Senuti to take songs from the iPod to a computer, then reformat and start a new library.

You could also use iPod-to-iPod to transfer the songs and delete them. Or use the Windows method.

What Skybolt said. I love Senuti (there are other programs like it too). I used it to copy over my whole library from my imac to my new macbook. And I used it to steal a few songs from my friend's ipod. You can just check off the one's you want and add em' to your library. It's easy =).

Hmm...
Do they make a program like Sentui for Windows Server?