secuirty

If their accessing the web its easy - in windows explorer go to windows - cookies folder - and check for any cookies with the dates and times you think someone is accessing your computer.

Otherwise as soon as you turn on your pc before accessing any programs - click on start - find - date tab - and search your hard drive(s) for any files modified on the dates you think someone is using it - it will list the times these files were last accessed/modified.

Look in the Document in the start menu and it will have every thing they did

I agree with Valiant, but if you want to prevent people from using the computer when you are not around or give access only to certain people you can set up a power on password in the bios setup screen. This will prevent the system from even loading until the password is given. Setting the supervisor password for the bios is also a good idea.

Ummmmm, DO WRITE THAT PASSWORD DOWN please though! Nothing worse to a tech than a BIOS Supervisor's password lost later.

Why not just install a keystroke logger like American Family, then you not only know when, but what they are using it for exactly. Then again, do you really want to know the entire truth?