Usually, you can use 32bit (x86) driver.
If you know that you need 64 bit (x64) driver, please use x64 driver.

32bit(x86) drivers covers
  Windows 2000
  Windows XP
  Windows Vista
  Windows Server 2003

64bit(x64) drivers cover
  Windows XP x64
  Windows Vista x64
  Windows Server 2003 x64