Never said the HP had no lag, just much less (i.e. noticeable) than the Dell. All LCDs have some lag, some more than others and the HP is a one of those that has a lot even the latest A01 version which I had.
try lcd24-7.info for a collection of reviews and news on 24" lcd screens. Plenty of reviews on both.
I never noticed any lag with 2408wfp at school. I used it briefly for browsing internet and played broodwar.
I think it's more of a draw picking a monitor with less or more lag. I know some people are going crazy over their 2408 because of lag.
Not all monitors are same from my experience, and I did notice those with multimedia interfaces generally have more lag than the other.