We're a little over 6 weeks away from the PC launch of Street Fighter IV and Capcom have released the required specifications, fortunately they aren't all that high and even a quite modest PC should be able to run it without too much trouble. I'd suggest that it will probably play much better if you use an Xbox 360 controlled though.

Minimum

OS: Windows XP
CPU: Intel Pentium4 2.0GHz or higher
RAM: 1GB or higher
HDD: 10GB of free space or more
Video Card: DirectX 9.0c/Shader3.0 or higher compatible, NVIDIA GeForce6600 series, ATI Radeon(TM) X1600 or higher or higher, VRAM ?256MB or higher
Sound: DirectSound compatible, DirectX 9.0c (or higher) compatible
Input Devices: Mouse, Keyboard

Maximum

OS: Windows Vista
CPU: Intel Core2Duo 2.0GHz or higher
RAM: 2GB or higher
HDD: 10GB of free space or more
Video Card: DirectX 9.0c/Shader3.0 or higher compatible, NVIDIA GeForce8600 series or higher, ATI Radeon(TM) X 1900 or higher, VRAM ?512MB or higher
Sound: DirectSound compatible, DirectX 9.0c (or higher) compatible
Input Devices: Gamepad ?Xbox360 Controller for Windows