What kind of windows partition is it? If it's FAT32 (windows 95/98/ME) then you can usually just mount the partition and copy what you want. If it's NTFS, then that gets a little more difficult.
If it's NTFS, you can do a few things (in my opinion):
1) Install Dapper and make sure that you select to NOT overwrite the existing /home partition. I wouldn't recommend this option (plus you should backup stuff anyway).
2) Follow
this guide and do a dist-upgrade.
3) download GParted Live CD and shrink the NTFS partition. Then create a shared FAT32 partition (or just an ext3 partition) in the empty space on the second drive that you can mount and store your files on.