I assume you're usin DDR ram since I don't know an AXP motherboard that doesn't require it.
Some motherboards can be
incredibly touchy about ram. Bluescreening/lockups/reboots trying to load XP is a classic symptom of the board not liking your ram.
Now, if you didn't know, your ram speed is linked to your front side bus speed - decrease the fsb to 100(/200) like you have done and you also bring the ram down from PC333 to PC266 - assuming you have PC333 ram.
Without getting too technical, in order to be able to support PC333 ram you have to effectively 'overclock' the bus between cpu and ram, since the max fsb speed is 266Mhz and we want 333Mhz. The get-around is a multiplier setting.
To support PC333, the multiplier is set to a 4:5 ratio ((266/4)*5 = 333 when rounded up). Why am I telling you this? Some motherboards allow you to manually controll the multiplier in case you want to bring down your ram to the slower speed. For example, on my Asus board there is an option in the bios called CPU/Memory Ratio, which can be set to 1:1, 4:5, or auto. If it is there and you have PC333 ram, set it to 1:1 to bring the ram down to 266Mhz.
While you may think this is going to impact your performance - think again.
Even if the ram is hopping along at 333Mhz, the processor bus speed is 266Mhz so the cpu can't keep up with the ram. Since throughput from the cpu to the ram and the ram to the cpu is the major deciding factor with ram vs. cpu performance, PC333 ram brings very little benefit to the system (it may be able to 'find' data slightly faster, but thats it).
I am running my Crucial PC333 ram at PC266 speeds because even my Asus board doesn't seem to like it at the higher speed - it doesn't crash during boot but does during games.
In fact, a couple of benchmarks on the system showed that ram performace was actually better at PC266 speeds with all the latency settings turned down to minimum (it's crucial ram so should be able to handle it) than at PC333 speeds at normal settings.
That may or may not be your problem, but it sounds quite likely to me.
ps. Most Asus boards should be ok with PC333 ram. However, I was daft enough to buy the board before reading the reviews, as it was on special offer. looking at the reviews, that was probably the
reason it was on special offer.
Type Asus A7V333 problems into google and you'll see what I mean.