I can't really help with your particular problem (never partitioned before - I don't think it's worth splitting up my 3GB drive...) but can you not just yank out the HDD and fit it as a slave in your new one?
You'll then be able to access the files on both, and if you wanted to reformat that drive you'll have extra space (perhaps it may be useful as a backup drive to keep the important stuff in case the new one dies?)
It's what I'd personally do, but bar that I can't be of much help.
Sorry 'bout that.