The system requirements for Resurrection of Evil are the same as DOOM 3 itself, basically if you can play DOOM 3 it's likely you'll have no trouble with the expansion pack.

Minimum:
P4 1.5Ghz CPU (or equivalent).
384MB of RAM.
64MB graphics card (see below for chip details).
2GB of free hard drive space.

Lowest supported GPU is a Geforce 4 MX (worse than Geforce 3).
Supported cards:
GF 4 MX.
GF 3.
GF 4.
GF FX (and higher).
Radeon 8500s, 9000s and higher.