At the risk of repeating myself...
The time has come where some games are finally starting to stress the AGP 4X spec. If you have AGP 2X on your board, I wouldn't really recommend dropping a GF4Ti in it. Secondly, the 4400 and 4600 both use new low-voltage designs. The 4200 uses the GF3s power-guzzling power architecture - so you might wanna check out first to make sure if your board can support both 3.3V and 5V current.
If you have a 1Ghz CPU or less, you MIGHT wanna think about dropping in a 1700+ (or at LEAST a 1.3Ghz TBird) or 1.6A Willie (for you Socket 423 users you're kinda SOL) in addition to the 4200. ALL the Ti's eat as much processor power as you can feed it. The faster the CPU, the more polygons it can draw per cycle, the more polygons, the more performance you get out of the 4200. But PLEASE, don't pair this thing with anything less than a Duron 800 or Coppermine 866. The gains you'll see performance-wise will be negligible if you're coming from a GF3, and all you'll notice if coming from previous generations is a slight speed boost and prettier displays.
Overclocking the Tis doesn't get you much in the way of performance increases. Visiontek covers their cards for their LIFETIME...don't screw that up by epoxying ramsinks on there just to get one or three more FPS. Video cards are the third hardest worked devices in your system after the CPU and Hard Disks. Having two that have failed on me when I DIDN'T overclock them, I can say it IS a pain when they go down.