I'm facing the same problem, and finally i made it after 2.5 days

I have Windows 7 -x86

Just follow these steps:

1. Install SQL Server 2005 SP3 -(SQLServer2005SP3-KB955706-x86-ENU)

2. Install P6 as a standalone.

3. Do not install sample Projects.

After installing reboot your PC. Try to login with User- admin Password- admin.

Enjoy i Veliki Pozdrav iz Srbije -Greetings from Serbia