Rands, re: OS-independent storage in a previous entry (guessing you may not read back!):

Both XP and OSX do SMB/CIFS just dandily. Windows file sharing will do the serving on XP, and Samba will do the serving on OSX.

You can also do WebDAV, which has seamless support on both platforms! As far as serving it, Apache can do the job (un-easy). Your good ol' iDisk uses WebDAV. In Windows adding a DAV share can be done by adding a "my network place." Etc.