I don't recommend using up all 4 primary partition slots. I'd use 2 of them -

1) NTFS for XP, and
2) Extended for Linux.

The extended partition can then be subdivided as mentioned previously. Thus, you can later (after Windows 8 comes out?) allocate another primary partition simply by resizing the / partition (make it last, to simplify resizing) and add the requisite additional partition.

Cheers!
Krishna