There are a number of different software programs that could be installed to record your keystrokes (i.e. everything you have typed) for later viewing. Some of them will even send your keystrokes to a specified email address so the person who installed the software does not have to return to the pc to view the keystrokes. These programs are sometimes referred to as "key loggers". There are also key loggers that are not installed as software but rather attach between your keyboard cable and the pc. All the keystrokes are stored on the physical device for later viewing. The advantage of the latter type of key logger is that the person does not have to install any software. Most key loggers are designed to be "stealthy" so that the user does not know they are installed. They don't show up when you select Start -> Programs or when you viewed installed software by selecting "Start -> Control Panel -> Add or Remove Programs".
In the pc security world there is a saying that "if you let someone touch your computer, it is no longer your computer". This means that if someone has physical access to your computer they can install whatever software they want. Even of the pc is password protected a person with the right know how (and this know how is readily available on the Internet) can bypass this security and install software.
If I was in your situation and I was worried about some type of spy software installed I would backup all my data files and email files to CDROM and have the pc software rebuilt from the operating system up. Then I would not allow anyone I didn't trust to physically access the pc. Unfortunately this is an easy task for a pc nerd but an onerous task for a non pc nerd. Maybe you can have someone help you with it. Just make sure you have all your important files backed up on CDROM before starting because everything will be lost on the pc once you rebuild.
Secondly I would not allow the use of the web cam. Disconnect it and don't reinstall the software for it if you rebuild the pc. By the way web cams usually require supporting software so I guess your H did install something on the pc after all.
