OK It's Sorted. Thanks for all the help.
In the end it all came down to incompatible ram.
I replaced the 2gigs of 266mhz with 4 gigs of 400mhz.
The whole system runs great now and cuts through big files on CS4 apps like butter...
Thanks go out to everyone who helped with suggestions with my problem solving hitlist.
This is BIG G, last survivor of the Nostromo, signing off.