The onboard 3132 controller supports the 2x eSATA ports at the back panel. So the fact that its external, and only 2 ports basically answers your question.
The nvidia controller has 6 ports (internal). I've got 2 raptors (ports 1 & 2) in raid0 and another 2 500gb's in raid1 (ports 3 and 4) with no problems. Performance was as expected when tested with HDTach.
Keep in mind, when loading your OS, (I'm assuming you're using some form of XP), you may have to for it to load properly. I used nLite v1.2.1 found here:
http://www.nliteos.com/
http://www.xtremesystems.org/forums/...4&postcount=85