If it had RAID, they would advertise it, so if you don't see it, it's not there
The G31 is basically an entry level on-board graphics chipset, and while the RAID is controlled by the southbridge, the chances of Asus pairing a low end north with a high end southbridge are quite low.
The Intel chip you want on the southbridge will have an R after it, e.g. ICH9R or ICH10R. The 'R' being for 'RAID'. Your board seems to have an ICH7 (older generation non-RAID).
The only Gxx series Asus board I found on their website with raid is the P5Q-EM, it uses a G45 northbridge and ICH10R southbridge.
You can view and compare the full range of Asus on www.asus.com.
Best of luck