Since you are on WC, +.5 is okay but I wouldn't push it past there even if temps. are within acceptable levels. There should be an option to change chipset voltage in your BIOS; the default value is 1.5V and depending on the board it may let you set it as high as 1.8V (this is from my experiences with the nforce chip).
Your BIOS should also have the option to set dividers; they are usually rapresented as frequency intervals (200MHz, 166MHz, 133MHz, etc.) or ratio type values between your CPU FSB and your RAM frequency (1:1, 2:1, etc.). This means that a 200Mhz or 1:1 divider will allow you to run both your CPU FSB and RAM at the same frequency (if the CPU is running at 166 so will the RAM), or similarly if running a 2:1 divider with a 200FSB means your RAM will run at 100MHz. Dividers allow you to set your FSB higher while keeping your RAM at it's rated speed or close to it (this reduces instability on the part of the RAM).
Everytime you increase or decrease the system FSB, you also change the frequency of the PCI, AGP, and IDE bus (SATA bus in newer boards also), which may cause instability with devices using those channels (video cards, sound cards, HDDs). Some motherboards (specially the nforce based ones) allow you to manually lock these or do it automatically. I remember hearing that one of the reasons VIA chips sucked at OCing was because they did not have this particular lock.
Of course, this is all from my OCing experiences with nforce boards, since the only VIA boards I ever touched were budget builds I did for others. You may be limited on your OC potential simply because you have a VIA chip, but you should be able to push at least a 300MHz+ OC.http://www.overclock.net/overclock.p...king-guide.htmhttp://www.overclock.net/faqs/31782-...pu-memory.html
Edit: That PSU looks a bit iffy, specially if running a WC setup and OCing. That may be holding you back too. Check the rails; you should have at least 20A in the 12V rail.