There isn't much of a difference in oc'ing the processor. The main factor you have to take into account is the DDR2 ram, it runs at much higher latencies than DDR.
Still, the process is basically the same. Lock your pci and pci-express buses, increase the HTT frequency of the chip 1 mhz at a time and reboot. If you start having trouble, do one of three things. 1)Lower the HTT multiplier, 2)Increase the latency of the ram, or 3)Increasing the voltage.
The most dangerous part of overclocking is increasing the voltage, that is where you could fry your chip. After you overclock to a level that you are happy with, run Prime95 on it for 24 or so hours. If any errors appear, it means the chip is not stable, so lower the speed and run Prime95 again.
Skim through the guide, like I said, the concept of overclocking remains the same even with DDR2. I do not however, know the safe voltage range for the Orleans chip, so I can't help you there.
I just ordered pretty much an identical rig except with some Corsair memory and the SLI version of the mobo. I also ordered a Zalman CNPS9500. How high it will go depends on how high the mobo will let you raise the FSB and how well you can manage the heat - I'm hoping to be able to get it up to 333 (with an increase in voltage), although that's probably just wishful thinking. 333 because that gives you 3000 with a 9x multipler and 1000 HTT with a 3x. This is the only guide I found for OCing the 3500, and while not great it's the only one I found. Please PM me/post the results of your OCing adventure