I had the same problems with display corruption and network probs after putting the FSB up to arround 155. I think it is something to do with the XP333r not automatically setting the PCI bus dividers correctly. If you set the PCI divider from 'AUTO' to clk/6 to start with and then work back from there if all is OK.
My PCI vid card seems to bomb out only a little over 33mhz on the PCI bus, so it was a case of working out the required FSB and selecting an appropriate PCI divider to get to arround the 33 megs mark. You can actually work the required settings out, for example 160/5=32 which is near as damnit to the spec of PCI.
I am awaiting delivery of my new Geforce vid card, so hopefully I will be able to wind things up a little more again with the new card.