That machine was a fairly high-end workstation machine a few years ago, and because of that they have specified ECC memory. This is error correcting stuff you usually only see in servers, and really isn't needed, it wont really help you any. And it's mind-numbingly expensive.
What I would do is rip out what is in there, and replace with this:
http://playtech.co.nz/afawcs0139235/CATID=252/ID=633/SID=160342863/productdetails.html
4gb DDR2 for $210 inclusive.
However: if you're only running 32bit Windows, you will only be able to use 3.25gb of that 4gb. Sooooooo - adding more RAM would probably help, but it would be only a bandaid.
Cheap way forward:
Upgrade the RAM ($210 inc)
Upgrade to 64-bit Windows 7 ($250ish) (and assuming your CPU will support it)
Longer term, less fucking around way:
Buy a new damn machine :>
Brand name, I'd get something like this:
http://www1.ap.dell.com/nz/en/business/vostrodt/vostro-430/pd.aspx?refid=vostro-430&s=bsd&cs=nzbsd1
The left one (upgraded to 4gb+ RAM) if you want to try and keep costs down, the right one if you want uber-speed.
Locally, Playtech are good people.
http://playtech.co.nz/afawcs0139235/CATID=140/ID=13327/SID=125927055/productdetails.html
or talk to them and they will build to order if you want an i7 machine.