How to tell if i get input lag.

Just got my 24" ( its the ebuyer ~£200) and i seem to either just be playing really badly, or getting input lag.

My FPS is 80-150 on CS:S which is my main game but i get little millisecond stopages and my aim seems to be terrible, I seem to get way less hits than it looks like I'm getting.
Is there anyway to tell whether its me or the monitor?


Thanks.

I would go to 2D and drag windows around. It should become apparent if it's lagging.

Like this
http://www.youtube.com/watch?v=TnApFzmd9NY

It'll be easier if you have another monitor to test against :)