i did a google search and found this for you if it helps


Doom 3 System Requirements


Minimum Specifications

* A 1.5-gigahertz Intel Pentium 4 chip or AMD Athlon 1500.
* 384 megabytes of memory.
* Two gigabytes of hard drive space.
* An nVidia GeForce 3 graphics card or better; or an ATI Technologies 8500 or better.

Recommended Specifications

* 2Ghz CPU or AMD 2500+
* 512 megabytes of memory.
* Two gigabytes of hard drive space.
* Radeon 9700 or an nVidia GeForce4 ti4600 graphics card or better.
* 5.1 surround sound audio


Worry Free Specifications

* 3 Ghz Intel Pentium 4 chip or AMD Athlon 64 3000+.
* 1 gigabyte of memory.
* Two gigabytes of hard drive space.
* An nVidia 6800 graphics card or an ATI X800XT
* 6.1 surround sound audio


The Lowest supported GPU is a Geforce 4 MX (which is even lower performing than a Geforce 3).

Supported video cards will be:
GF 4MX
GF 3
GF 4
GF FX 5X00 series and higher
RADEON 8500s, 9000s and higher


In PC Gamer's Exclusive world premiere review, they recommend at least:

Any 2Ghz CPU.
512MB RAM.
Radeon 9800 or equiv (ie FX5900)
5-channel sound card and speakers.