yes. linux and freebsd can share swap
http://www.linux.org/docs/ldp/howto/mini/Linux+FreeBSD-3.html
but it doesn't help you out(and no longer necessary).
you have at most 4 primary partitions on a disk.
1. you can have winxp and win98 in the same partition (if you choose vfat32);
2. and you need a small primary partition for /boot of linux;
3. a ext2/3 partition for linux.
4. a swap for linux
5. although freebsd can squeeze into one single partition, including swap, you don't have this last one.
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