Minimum requirements for Fallout 3 are:
CPU: 2.4 Ghz Intel Pentium 4 or equivalent processor
RAM: 1GB System RAM (XP)/ 2GB System RAM (Vista)
OS: Windows XP/Vista
Video Card: Direct X 9.0c compliant video card with 256MB RAM (NVIDIA 6800 or better/ATI X850 or better)
and for fallout NV:
CPU Speed: Dual Core 2.0 GHz Processor or better
RAM: 2 GB
OS: Windows 7 / Vista / XP
Video Card: NVIDIA GeForce 6 series or better, ATI Radeon X1300 XT series or better
Free Disk Space: 10 GB
So you could run Fallout 3 atleast, but for Fallout NV you would need more ram to meet the minimum requirements.