Alright, what I did was install Win7, partition, then install OSX, but (I think) this will work for OSX then WinXP. Also, I'm feeling lazy as to exact details, but everything can be searched for online fairly easily. This assumes you don't have an external dvd drive (just as I didn't), but you have at least a 4GB flash drive (a smaller one and a larger one in addition to the 4GB makes things a bit easier)
Make a bootable flash drive using old windows 98 files, press esc key when the eeepc bios screen pops up, select the flash drive.
You'll see a cmd prompt. Set the partition active that you want to install WinXP on (s0d2, I assume)
Copy the WinXP cd to the flash drive, boot from it again, install XP.
Do w/e on XP (update/install drivers, etc). When you're ready, make another flash drive/use the same to do the Win98 thing again, change active partition to the OSX one.
Boot into OSX, install Chameleon 2.0 RC2 (or w/e is newest).
Now see what happens. Hopefully it should show both operating systems. If not, you may need to repair the MBR for WinXP WHILE THE WINXP PARTITION IS ACTIVE, then activate the OSX partition and test.
This took me a lot of time to get everything working, but boy did I learn a lot. It was fun, too!