If you can find one with exactly the same stepping number, you can buy one CPU.  More likely you'll need to buy a pair of matched processors and replace the existing one.

Thanks for that ejn.  I have found this matched pair:

Intel Xeon 3.2Ghz - Socket 604 - 3200DP/1Mb/533/1.525v

Will they be OK to fit into the 1750?

Cheers

Paul