I'm running Mandrake 10.0 and want to add windows xp to my box. Root is mounted on HDA6 and my home directory is mounted on HDB6. Can I just resize the partitons (I have a partition, HDA1 that is 6 gigs, unmounted) on my first drive, install windows, then reinstall Mandrake and have the dirs mounted in the same place? And if I use the same username will it overwrite my home directory?

You will only need to boot to rescue mode and reinstall the Linux bootloader (Lilo or Grub). No need to do a full reinstall if you don't feel like it.

You don't have to reinstall Mandrake afterwards, make sure you have a Mandrake bootdisk, install Windows if you really have to and then boot with your Mandrake bootdisk and reinstall your bootloader - grub or lillo, dunno which one Mandrake uses but I guess grub.

I think mandrake used lilo, but if you are using grub, put a floppy in, and run in the terminal as root (login as root, not su in terminal)

grub-install /dev/fd0

this will install grub to the floppy - just test it boots to make sure (with floppy boot set first in the bios of course)
after you install windows use the floppy to boot the computer into linux run

grub-install /dev/hda (replace hda with the hard disk linux boots from)
the you need to reconfigure grub to boot windows for you

if you're on lilo tho, I dont know, but if you google "make lilo boot floppy" or something like im sure you'd find something

good luck