The memory specifications for your desktop should be found at the desktop maker's website. If the memory meets those specifications, then it should be compatible. Compatibility with the desktop, however, doesn't necessarily mean that it will work well with other memory modules in the desktop.
What can you tell us about the following:
Proliant server model
Proliant server motherboard model.
Model number of the server RAM.
Desktop make & model.
Desktop motherboard model.
CPU-Z may help to ID all of the above.
Say I got some Compaq Proliant server RAM and I wanted to put it in my desktop (512 MB PC 133 168pin Dimm) everything matches. How do I know if it's going to work or not?