This is just imo, but if upgrade the CPU or the graphics card (one but
not the other) you'll still be disappointed.
Assuming your mobo can take say a 3.0 or 3.2 P4 that'll cost you about
150 ish too, but you'd probably get more of a boost by spending your
150 on a low-spec (ie features) but top-range (ie GPU) graphics card.
I guess you'll probably end up wanting to upgrade both assuming your
motherboard allows for it.
I went through a similar upgrade a while back. I had an Athlon XP2000 &
Gf4200, I bought my current XP3000 to replace it & although 3dmark &
everything said my PC was faster, it didn't feel much different.
Eventually I upgraded the graphics to a 5900 & right now everything is
good. Tried the old XP2000 with the 5900 & it was subjective, but of the
two 120-odd upgrades the graphics card gave more of a boost on it's
own, but both together transformed my PC.
You have a good match with your 2.2 P4 & 4200 and either a CPU or
graphics card would be a good choice, but if it were my system I'd get
the graphics card first but only as the first part of a two-part
upgrade. 512Mb RAM is fine, but then RAM is cheap so upgrade that if you
find you need it as & when.
If your mobo won't take a faster CPU (or not enough of a step up to make
it worthwhile) you're looking at another 80-100 for that plus major
surgery on your PC. If you are at the stage where you are considering a
mobo, CPU & graphics card upgrade you may as well wait to for it all in
one go & take advantage of the latest technology. If you only plan to
change one thing though, graphics card is the way to go imo.
Malc.