Mac,
An alternative to making up a Windows boot floppy would be using a Knoppix Linux CD. Never tried it, but I understand it's a full Linux distro that boots off the CD and would therefore (I assume) allow you to run Samba to mount the remote drive. Actual copying of partitions could be done using the "dd" command. You'll find it on knoppix.com. I'm downloading it now so if you want I can report back on how well it seems to work as a bootable environment. Don't expect me to start copying partitions around!
I'd still copy direct from old disk to new disk rather than via another machine...
One possible "gotcha" that nobody seems to have mentioned so far is Windows XP product activation - "If you overhaul your computer by replacing a substantial number of hardware components, it may appear to be a different PC. You may have to reactivate Windows XP" says M$.