The System Requirements for RoE will most likely be 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.
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).
GF 4 MX.
GF FX (and higher).
Radeon 8500s, 9000s and higher.