IPod troubles, HELP!?

Ive got an ipod nano that ive had for a while on my Mac in the UK. I recently moved to Thailand and took all my music with me, but not my mac, and am now using a windows. Is there a way to put new music on my ipod without wiping the old stuff away? The computer is recognizing the iPod is there but I cant use it, how do I install without an installation disc?