It may be for "your PC", but you're likely using it to check on someone else using said PC. Right?
It's ok, I busted my wife chatting it up with a dork on MySpace earlier this year and cut that crap off before it went anywhere. We got some help and are working it out, so I have no regrets or moral qualms.
Anyway, I'm not going to troll in here with that stupid story without offering some advice based on my own experience. If you run an active AV shield that scans continuously, you're going to have headaches installing and running keylogging software. I got a software keylogger from a shady source, and got bit in the butt for lowering my AV shield. Seems it had a trojan in it too.
A cheap hardware logger, like one that is a keyboard wedge might be better.