it wont by much. especially considering most games can still take full advantage of only one core, and even then, the performance improvement from 1 to 2 or more cores isnt huge for gaming yet, youll still be limited by the gpu most times, unless you turn your resolution and details down. then your max fps will be limited by the cpu more.
otherwise, again, no.
@systemlord... a P4 at 3.0 is only going to be fast enough to run smoothly at lower settings as you saw, since its performance is noticably lower than a 2.4 4000+. a P4 3.0 is more or less on par with a s462 3000+ @ 2.0 that a relative has (which is also poor for gaming), since they were released around the same time too.
to give an example, the X2 3800+ i have, is still fast enough to play older and newer games pretty easily, @ stock even (my 7800GT 256 is beginning to be overwhelmed a bit though). the biggest improvement however, is going to be in the amount of memory the OP has, if the OP has less than 2GB of ram, then thatll end up being a problem for gaming most times now, much more than their cpu will be.