There may be an issue with the computer hardware, not software that's causing the issues you've been having.
I was gonna post the same comment. Do a clean install of Snow Leopard, and upgrade to 10.6.2. Run a few system tests. It may be a faulty install of Snow Leopard (more often it's PEBKAC, Problem Exists Between Keyboard and Chair) as clean installs usually rectify the issue(s) (maybe from another third party software application, which happens A LOT, or a corrupted kernel or .plist, who knows).