I'll stick the swap/virtual/paging (how many names are there for this?) files on the master drive. I have 1024mb of RAM, so the Windows swap file should be what? Double that? Half that?

I'll make a partition for each OS plus the boot partition. A backup partition for each OS (FAT 32). /home and /tmp will get there own partition also.

Can I do all this with Partition Magic?

I'm in the process of formatting both hard disks right now. I should have XP up and running by the time you read this. Hopefully I'll start installing Gentoo tomorrow or Thursday.