Szymon Kobalczyk was having fun with the 64-bit version of Vista. That is until he tried to install a game called Price of Persia: the two thrones. The machine won't even boot now! But most likely all is not lost. If you find yourself in this kind of pickle then getting back to a restore point using System Restore is a great thing to try. Here's two ways to do that:
First plan of attack is to try to boot to Safe Mode, which is done from the boot menu that comes up by pressing F8 right after the POST initialization is done during the first part of boot. This is right after the machine beeps. (If your machine beeps during boot!) Once booted and logged on, you may want to try finding the specific driver that is giving all the grief and killing it. This can be done in MSCONFIG. But another more straightforward option is to bring the registry back into a previous state, which can be done with System Restore from Control Panel / Backup and Restore Center. The first task listed at the left should be the right one, "Repair Windows using System Restore". Pick the most recent entry, which should be right before you installed the bunged driver.
Another option to get into System Restore if even Safe Mode doesn't work is to boot with the Vista DVD, select your language, click "Install" (but don't worry, you won't really be doing an install), and then press SHIFT-F10. You'll be at a command prompt. (Or at least this works with the 32-bit version of Vista.) Type RSTRUI, and up should come the normal System Restore program, and it should be able to restore the SYSTEM hive of the registry back to what it should be.
There are many other utilities you can run when booted into the WinPE environment used by Vista's installer.