Sounds to me like you have either a bad kbd or a bad kbd driver. I would start by reinstalling the kbd driver and if the problem persists contact HP about replacing the kbd or sending the computer in for service.
I've got a weird one. On my HP Pavilion 7010US [WinXP Home] laptop when I run Excel  and use the arrow keys to navigate across cells, random characters are entered into the spreadsheet [particularly "c" and "8"]. I assumed it was the keyboard, so I replaced it. No luck. It still does it. I ran keyboard test freeware that I downloaded off of CNET and it does show the "c" key and others as being clicked when they aren't too. It doesn't do it with a USB keyboard, just the laptop keyboard. I can't seem to find any resources on this issue from Microsoft or HP. Any ideas?