Computer lags when typing in Outlook

OK, this might be a shot in the dark. A few months ago our company migrated from NT on the backend and 95 on the client to 2000 across the board. Since then there random, but consistant cases of users calling and saying that their computer will lag when they try and type something in Word or Outlook. I have seen this issue because it happens on my computer too. I will be typing in Outlook and all of a sudden nothing will happen at all and then a few seconds later, what I was typing will fly across the screen and everything will be back to normal.

We are running some special apps such as iManage and Norton Antivirus. I am thinking it could have something to do with Norton doing updates. However, it also could be a transport issue on our network. Anyone else experience this???

Thanks