Since HP never shipped this computer with Windows Server 2008 x64 installed, they do not support it in that OS. One of the first steps in finding drivers is to first identify the hardware.....
You might give Everest a try:
To find make and model of pc hardware, EVEREST Home Edition
is a free system diagnostics, system information program that will id most hardware onboard a mb. as well as the actual motherboard. It will, in some cases, actually provide a download link for the driver.
Alternate Everest download link: (offers 2 sites to dl program from)
Run the program and then:
Click on Computer
Click on Summary
Right hand window (hardware) if the text is BLUE
this is a link to the web site for that particular hardware.
If you have additional questions or need further help, please post a "copy and paste" of the COMPUTER SUMMARY report (Leave out the Debug–PCI section) from Everest.