The last part of your message implies that you have two machines, one linux and one XP. The first part of your message says "on a single machine" which implies that you are dual booting Linux / XP on the same machine. If you have two machines connected on the network, then install and configure Samba on the Linux machine, and share the folder you want to write to on the XP machine.
Look for a samba-doc package if it's available. It supplies a book "Samba3-ByExample" which has example samba setups you can base your configuration on. If you can't find such a package then go to the samba.org website. You can download it from their. I had purchased these books at a bookstore before I found that the same books. I don't mind the I supported Samba that way! I learned things about Windows networking I hadn't known before, such as how Win XP home edition won't work in a domain.
If you are dual booting, you can mount the windows NTFS partition in linux to read. I don't know how reliable writing is even if your kernel supports it. It may still be better to create a fat32 partition that both OS's can write to when you are dual booting.