typing error/moving cursor

while typing anything, my cursor jumps back to anywhere ive typed putting letters haphazardly amongst written sentences.

my cursor stays visible during typing and cursor seems to jump to its location. its driving me up the wall. am i doing something wrong? also the some letters and spaces dont appear-random!

my system is:

latitude d600

xppro up to date

1.6 centrino

40gb drive

2gb ram 

running firefox 2 and internet explorer

avg free spyware & anti virus

spybot search & destroy

peerguardian2