Sounds like you are wanting to use samba to share info between the machines. ALthough you don't mention what use you are putting the machines to. XP can't share files with linux as such, so you need to set up samba to do the work for it.
Note XP can't write to ext3, reiserfs. YOu can get Linux to write NTFS, but you need buld this into the kernel (you can compile a module). Anyway, what you describe shouldn't be too difficult.
and have a look at: SMB-HOWTO-html.tar.gz
As it's slack you will have to edit the files manually, but as there are only two PCs we're not talking a 5000 user domain here.
Basically, you need to have the samba daemons running on your linux pc and edit the samba config file appropriately. The howto guide will tell you a lot more than i can.