postgresql installation fails on windows 2000

Firstly, I am a complete newbie. I need to make the move from MS Access and am looking at either MySQL or PostgreSQL. However I cannot get postgresql to install. I get the following error message. "failed tocreate process for InitDB. Access is denied."
I have searched for and read a lot of information, I have set permissions and created users, all to no avail.
This is my last try. Can anybody give me a clear procedure that will solve this problem.

Thanks
Phil