If you do have environment variables referring to the Python Blender uses, then the simplest solution is to create a batch file for launching Blender, add the relevant SET commands for the env variables and then remove them from the global environment.

Which version of Blender are you using (I'm guessing 2.49 as that uses Python 2.6) ?
Perhaps more importantly, are you using the 32-bit or 64-bit version ?
If you're using the 32-bit version, are you using the installer or the ZIP ?