You didn't say which sort of malware you were infected with, so the safest bet in this case is to treat the entire disk as infected.
Insert the hard disk back into the XP computer, and then on a good computer download and burn the F-Secure Rescue Disk
. Place that into the CDROM/DVD drive of the XP computer, and boot it up. Follow the prompts to scan for and attempt a repair for malware. Based on what it finds and is able to clean, you should be able to transfer these files to your new PC using an external enclosure.
I would not attempt a transfer from the XP disk to your new PC without knowing what malware you are dealing with.