how to lock out annoying guests

friend here needs some sort of a program to lock out his roomate from his computer. he logs on somehow and then downloads any and all kind of porn and viri. any suggestions on a good lockout program?

You can go the redundant route and take out the black power cord from the computer case.  This will essentially stop him from accessing the comp.  Is his OS windows?  I will assume that and say he should get the passworded logon screen....and I know he is using that and it is ineffective...but here is the thing...USE A PASS THAT IS NOT OBVIOUS.  I bet you the roomate has used a keylogger to find out all the pass info on your friend's comp, so I would suggest looking in the registry (advanced users only) and finding what the file is called.  Note:  This is an extremely hard, and final option to take.  Also I suggest Zonealarm in order to block against the viruses and the like.  Finally, kick the roomate's ass.