Most (abit, epox, asus, NOT msi) KT400 chipsets have been reported to allow access to the LOWER than 12 multis for the high speed tbreds.
As far as I can tell, most tbreds (2400 and up, 1700(A), mobile 1600(A)) ALL COME UNLOCKED, no bridge work. Now, for the 2400 and up, "unlocked" is suposed to mean all multis above 12.5 are available. So, the MSI is doing what its suposed to do, but only allowing 12.5, 13,13.5, etc. multis. BUT, for OCing, we want LOWER multis, so we can up the FSB. The abit, epox, and asus do this "lower multi unlocking" for us.
I believe even the kt333 or kt266a chipsets have all the multis already available for the lower speed tbreda's, e.g. the 1700.
I'm currently at 8 * 200fsb = 1600 mhz stable with an epox 8k9a, 1600xp MOBILE tbreda, and corsair xms 3200 ram, ULTRA mem settings (cas2).
The CPU is what's holding me back, needs extra juice just to get to 1600 mhz, NOT what I had expected from these mobile chips. :-(