PostGersql 9.00 beta4 the service user account postgres couldn't be created! HELP

hey
first time i installed pg at the end it show an error :
Problem running post-install step. Installation may not complete correctly. The database cluster initialisation failed.
i opened file bitrock_installer.log it showed cann't find registry key ... idk so i used CCLEANER and fixed all the registry issues .
then when i come to install it again it show me The service user account postgres couldn't be created !!!
how i do create it what to do ?
Please help!

Thanks.

ok this fixed i runned the it as administrator and it made it but the problem now this error came back :
Problem running post-install step. Installation may not complete correctly. The database cluster initialisation failed.
please guys what to do ?

ok looks like i fixed it my self ! the problem was the installed cann't give the data folder a permission on the installation folder so i gave it permission and now every thing works Great !

But interesting as how you do it? Interested in the details. Thank you for your response, understanding and cooperation.

I am having this same issue with the install failing to initialize the cluster. I am installing on OS X, Snow Leopard. I have tried both the 8.4 and 9.0 installer, and both have the same error at the end of install. I've checked the "data" folder, and it has Read & Write permissions for "postgres" - seems right to me. Anyone know the solution?