I need a processor for a mPGA478B socket on an Intel SL73Z motherboard from '02. Can anyone tell me what kind of processor I need? I have the socket part but not the processor.

SL73Z? Is that the board model or the spec code for the southbridge chipset on the board?

In any case, Intel's website has exact processor spec compatibility info for their motherboard+BIOS version. The board revision level can also be a factor as to which processors it supports. Strongly recommend this technical documentation is consulted before buying a processor but Netburst Celeron and Pentium 4 processors in the 1.5 - 3 GHz.-ish range fit these sockets.

Info:
Wikipedia: Socket 478

Thank you so much. I will look into it