get more memory.
Thats the first thing i would suggest. Having 256MB isnt good anymore, unless you are using Windows 2000 or below.
The requirements are:
Processor: 1.4 GHz
RAM: 256
Hard Drive Space: 5GB
Operating System: Windows 2000/XP
DirectX Version: 9.0c
also make sure your system is updated, with all the correct drivers, and DX installed. Checking for viruses really helps too.