Windows 7: Create a locked-down account for playing games only?

What would be the quickest way to create a completely locked-down account on my Windows 7 Home Premium so that my flatmates can play my Steam computer games without access to anything else? I've created an account and blocked it's access to the root of all drives via the Security tab of the Properties dialogue of each drive. I've also blocked access to all programs except steam.exe and associated programs.

The problems are:

some programs are set to run at start-up and yield an error for each program which cannot start - how can I disable start-up programs for a specific user account?

steam.exe cannot run because I've blocked access to the drive - I want to be able to block their access in Wndows Explorer but not the authorised programs' access; you know?

See method 2 option 1 in this tut to remove startup programs for a single user.

Startup Programs - Change

Explorer is the basic shell, disabling it will cause various problems. One option could be to try parental controls and block everything except steam and the games. Another option could be to use a separate partition or hard disk solely for games and nothing else.

Hi, thanks for your response, but I checked and both of these folders are empty already:

C:\Users\Games\AppData\Roaming\Microsoft\Windows\Start Menu\Programs\Startup
C:\Users\Games\AppData\Roaming\Microsoft\Windows\Start Menu\Programs\Startup

I think that the settings for these must be stored somewhere else. But how to access them?

Here's a screenshot of the errors: http://i.imgur.com/1YYhd.jpg

I think Microsoft should make it so that automated start-up of disabled programs is disabled.

What about enabling the Guest account, and using that? Would that suffice?