I've read of guys doing 800+mhz overclocks on those easily.
Here's a very helpful beginners guide.
After going through that (and the troubleshooting guide at the end)...
1. remove 2 sticks of ram, see if the 4x1 isn't causing your problem.
2. run orthos with everything at default.
3. If it fails, try swapping sticks of ram out, you may have a bad stick.
4. Just to be sure, it is the fsb you're changing, not the multiplier?