[Steven-n-Donna]

You will only see a difference if your current card only allows (horrific) 256 or 16 bit display. 24 bit is pretty clear, and it is hard to see a difference between 24 bit and 32 bit.
Another way to get more out of your display is increase the resolution to 800x600 or even better 1024x768, and if you can higher.
The only problem with that is you need a larger monitor with higher refresh rates. 19 or a 21 inch monitor gives you lots of viewing room. I run on a 21 inch viewsonic P-815 with a Revolution IV 32 meg video card. I run on 32 bit as well.
If you want the best increase of performance, you'll want a new processor and most likely a motherboard.
The way most motherBoards are laid out is everything is restricted on bandwidth in the North bridge processor. Most systems are a 100 to 133 mhz. Now if your proccessor is a 133mhz bus speed (not the processor clock speed). The ram runs on this same system. Your hard drive is limited to this bus speed as well.
If you want the greatest upgrade that you will actually beable to notice without breaking out some sort of diagnostic program, I'd go with an AMD processor and a Abit mother board with Raid onboard control.
With raid, you'll use 2 hard drives as one to double your bandwidth between the CPU, RAM, Cache, and video card to the hard drive.

Swaping a motherboard with the new guts on it is pretty easy, and most people can accomplish it with little problems.
You can overhaul any system practially for 400 to 500 bucks.
Then you'll get into overclocking, and spend half the day with the case off filling the water cooling radator back up with BeCool.

Steve