I can't seem to get my FSB of my Athlon XP "Barton" 2500+ to run at 200Mhz instead of stock 166. Is there any way to do so in KT400A boards? Or should I get another nForce2 Ultra to do it?

If this is feasible, some links would be appreciated.

check whether you've supplied enough cpu voltage

can you provide more details, is your processor unlocked? if its unlocked then by default your barton is clocked at 1.83GHz (166x11), so you try matching the speed back by setting it at 1.8(200x9) notice the multiplier is set to 9 instead of 11. If its bootable then tadaa u've it running at ddr400

Hmm... my m/b has no single option to change bus/multiplier ratios.
And from other online posts I see that only the KT600 supports 200 double pumped FSB- officially, at least.

Any applications to tweak the multiplier for the CPU (it's unlocked), however?

Till now, NOONE has a way to clock my mobo FSB (Gigabyte GA-7VAXP-A Ultra) to 200Mhz, the max they've managed to do is somewhere near 189Mhz or so...

Now I just need to tweak the multipliers to a safe yet resonably faster settings (currently 175 Mhz, X11 multiplier, in most terms it isn't even considered "overclock" )

175 x 11 = 1925 = barton 2600+.. overclock already.. ok what... hehe
maybe its your proc limit already?

As far as i know KT400A doesn't support FSB of 200Mhz

http://www.via.com.tw/en/products/chipsets/k7-series/kt400a/

incinerate is correct there. There's no way to tweak the multiplier through any applications. U hav to make sure that ur barton is <0340 step. However, i remembered there is a hard mod to the cpu for multiplier alteration, even if it's hard lock, but a very risky one.

Technically, the KT400A is able to do 200mhz easily. Heck even the KT266A does 200mhz (certain boards applied).

It depends on the board, and it's considered overclocking since KT400A doies not support 200MHZ FSB, only memory bus 200MHz (DDR400).

I don't like to overclock the FSB more than 166Mhz as doing so will end up overclocking the AGP and PCI buses as well. Instead, i unlock the multiplier of my Sempron 2200+ (166 x 9 = 1500Mhz), converting it to a mobile AthlonXP-M running at 166 x 13 = 2167Mhz using only stock cooler!

check also the pci lock or not..
can use clockgen..