If you check overclockers.com, out of the 2 ppl that entererd their OC, one was using a SiS 645 motherboard.
They had the processor set at 133mhz FSB x 16 to weight at what they said was 2133 (comes to 2128, but whos counting ) I'm guessing this person didn't really try to max their processor, and just set the FSB to 133mhz.
lookin4dlz
On the question of whether the SiS Ultra Mobo is compatible with the older gen of power supplies, I dont think it is (I'm pretty sure you're talking about the Asus model that has the 4pin connector along with the power supply). You could probably do one of two things, buy the Asus Mobo with the modified connections, which is about 30s more, or you can buy a new case and power supply combo which can run you around $60-$65 for a nice case at Newegg.com. What I would do is save up the 30 extra bucks, and upgrade to a new case and 300w power supply. If there is a Circuit City in your area and they have the 256MB PC2100 Centon ram in stock, you might be able to save the $30 off the ram and put it towards the case/power supply. And also, 235w really isn't alotta power (my system wasn't doing too good w/300w running 3HDS, AMD XP, DVD-Rom, and a CD-RW so I put in a 431w PS just to be safe).
So it could break down to this:
MSI SIS 645 Ultra Mobo + P4 1.6A Processor: ~$245 including shipping to NY
CircuitCity Centon 256MB PC2100 DDR : ~$48 including tax and shipping
Newegg.com EVERCASE E4252WEF25 w/ 300w Supply: $67 including shipping
Total: $360
or
Asus P4B266-C Mobo: $122
P4 1.6A Processor: ~$157
Crucial 256mb PC2100 DDR: ~$76 including tax (they tax me and I didn't even know they had a store in NY)
Total: $355
With the first option giving you a new case + psu, and the second option giving more reliable RAM w/ older case& psu.