Heya.
I just read your post and I'm going to look into it in a sec.
First I'd just like to give some other symptoms. This is mainly a list
of programs that the whole lag situation has been known to happen in.
There are probably more, but this list gives a general idea... They are
as follows:
Flash MX
Flash player (when viewing in a browser)
Photoshop
Graal (online game, see www.graalonline.com for details. !! This is one
that causes lag the easiest !!)
Worms World Party / Worms Armageddon (More games. These also cause it
rather quickly)

It is mainly games and graphic intense programs and those with a lot of
virtual memory usage, which first lead me to believe it was a problem
with my RAM. However, I have bought new RAM and still suffer the issue
(UNLESS, my RAM is configured incorrectly. If so, how would I correct
that?). I then thought it was my graphics card. However... If that's
the case, surely the lag would be immediate?
So now I'm stumped and asking others

I'll get back to you soon in response to your post w_tom.