For years I was always scared to OC a pc because of the cost involved, until now. I did alot of reasearch in the years following my first comp purchase in '96'. Then I got my A+ and was still not too confident in OCing a comp.
I read Tom's review here: http://www.tomshardware.com/2006/0 [...] ghz_cores/
I thought for that price I would give it a go and had very good results but, haven't tried water cooling yet.

USD Prices
Abit FP-IN9 SLI ($135.00)
Cooler Master X Dream P775 CPU Cooler ($20.00)
Pentium D 805 2.66mhz (same as the review) $45.00
Corsair Value Select Kit 2x1gb 667 DDR2 ($63.00)
PNY Verto 8500 GT 512MB PCIE ($115.00)

I went straight for the 1mhz jump in the cpu and to my suprize, it works!

Like Tom said the multiplier is 20x. I changed the FSB to 720 and got 3600.0 out of this cpu without changing the voltages, extra cooling and 1:1 memory timings. I ran memtest for 13 hrs without a single error but, when I run Prime95 or 2004 I get errors. I also tried CPU Stability Test 6.0 and it reboots the computer.
http://travel.webshots.com/album/561904441OAWIRw

If you have ANY comments on making some changes to to get this to run Prime95/2004, I would appreciate hearing from you.

Raise the voltages?

Although deemed stable by memtest, could be ram getting too much or not enough voltage.