ihave this new keyboard that whenever i am playing an FPS or any game where my movement is controlled by WASD on my keyboard, my movements are carried over.
Yup.. same here. On 2 seperate occassions now. I agree with all the above mentioned also but... here's what i found out plus, a newer twist on keyboard"ghosting".
I had added a wireless-logi-game pad to my hardwares to game with once and yikes! in comes the ghosting probs on my WASD inputs like you found. Looked into all kinds of info's and tried a bunch too.
Then i found my answer... it was the added wireless-controller. Almost all wireless-input devices, use pretty much the very same frequency(forgot the number that designates it)and once i unplugged and removed and battery power to the game pad the wireless-keyboard worked great! WASD inputs and all... it all whent back to normal once again for the longest time. Months and months im saying here.
However..
Now for the twist.
Since Dec.23.08 on I've switched over from a Cable ISP to a DSL ISP.. started up a FPS game and played for a week and im now ghosting all over the maps.

I tried a brand new CABLE-MS keyboard with USB...nothing but ghosting... tried connnecting a 3rd k/board with a P2-keyboard connection on it ... again nothing but ghosting... therefore i've now returned that "newly bought k/board" and have reinstalled and now gone back to my original MSwireless-K/board. I'm still scratching my head because all the 3 boards, the cable and wireless types are ghosting... huh!? The games are based on the "Left 4 Dead"- running on "STEAM" .. and the other is BF2(BattleField 2) that im also ghosting on.(EA games)
Now im thinking about the SP's provided DSL Wireless Modem... but, nah! Couldn't be a frequency thing with that cause the 2 wired-k/boards were ghosting too.??
I'm about ready to clean off the ol' HD and reload XP and start fresh again and just cross my fingers that the renewed installed XP files will fix my ghosting probs.
BTW... For about 2-3 days and very close to the same time as the ghosting... i was running my comp a bit hot cause .. DUHHHHHH.. i had by accident reinstalled my exhaust fan backwards and the comp was running a little extra warm for a few days.
Still thats been fixed now and yes, im still ghosting on my favorite FPS maps and games.
So there you have it. A possible solution and yet a new twisted version to those same symptoms.
Anyone got any solutions and ideas here??