If you have a T&L capable video card with at least 32 MB of video RAM then you need at least:
800 MHz processor or better
256 MB RAM if Windows XP, Windows ME, Windows 98 or Windows 2000
At least 3.5 GB of hard drive space
If you have a non-T&L capable video card (an Intel Extreme Graphics or a Radeon 7000/VE Series) then you need at least:
2.0 GHz processor or better
256 MB RAM if Windows XP, Windows ME, Windows 98, or Windows 2000
At least 3.5 GB of hard drive space