I've got the same setup, and the same problem, except I have a 1700+ at 147 FSB and that posts as a 2000+. (even though it only runs at 1617mhz)
It isn't as easy to up the voltage on the XPs 'cos of the weird bridges, but I think the pattern for the voltage is still the same. Try setting it to 100/150 and see if the RAM fails you.