I'm not 100% sure if I'm correct but I'll give it a try.
For the mobo it says:
"Four memory banks using two 184-pin unbuffered DDR 333/266/200 DIMMS"
And the memory is 184-pin, but it's DDR 400 so it is not compatible, it might fit and even work but not with full capacity.
All you need to do is look for the pc1600(200) or
pc2100 (266) or pc2700 (333) all DDR memory in the size that you want to use up to 2 gigs.. You shouldn't need that much as I think it would be a waste of money.
I am not sure of what speed that you now have in your computer.
I would look to have installed 2 sticks of 512 mb of non ECC pc2700 DDR memory of a major brand name such as the corsair or compatable. And I wouldn't even bother with that HP brand that is already installed. Just remove it and store it for emergency usage.