Cursor skipping is making me curse!

Here's what happens:

When I type a sentence like "Dell hasn't been able to fix my Inspiron 9100 laptop.", the cursor jumps backward into the middle of the sentence while I am typing, so when I am done the sentence looks like "Dell hasn't beenmy Inspiron 9100 laptop.able to fix"

It happens regardless of what application I use, powerpoint, excel, word, outlook, message boards, etc. During a full page of typing, it happens one to three times.

I am using a Dell Inspiron 9100 which is running Windows XP.

The cursor does not skip if use an external keyboard.

It has been suggested that maybe I am hitting the mouse pad by accident when I type. I have tried to watch for that and it doesn't seem to be related. When I type, I will occasionally miss, and tap 2 keys at the same time. However, I tend to doubt this answer because I have had the computer for several years and haven't had this problem until recently. Last spring my sound card failed and Dell sent somebody out to replace it. That's around the same time my cursor started skipping.

The first time I contacted Dell they checked the bios and ran some cleanup utility which seemed to work . . . for about 8 hours.

Since then Dell has replaced the keyboard, the fans, the soundboard(again) and the motherboard (twice). The last time, instead of sending the service tech out to me, the asked me to send the computer to them.

After each service attempt the problem would go away, only to resurface within several weeks.

Thank you for taking the time to read my post. Any thoughts on what could be causing this?