It doesn't have a video card at all, it has a graphics controller??? I'm at work so can't get the actual info, but that's what the guy at thq said.
Apart from your onboard solution possibly being rather outdated, it will do the exact same as any expansion videocard. That guy at THQ was probably getting high on some kind of home brewn experiment, best not listen to people like that. I hope you're teaching your kids to say no to drugs or they'll end up giving advise just like that.
If you want to play games on your machine, you're probably going to have to add more memory. 256 is very little, even when you just run Windows XP. However, if you're not going to take that advise, don't look surprised if your kid tells you the computer is too slow to run the games regardless of that new videocard or not.
As for the videocard; if you know the differences between 2x, 4x and 8x AGP cards or PCI-E/PCI, how to handle electrostatic discharge and install the latest drivers, then installing one is a piece of cake.
My guess is that you don't so lets get some more information;
Can you tell me the name of your mainboard? That way I can look up the type of your card you will have to install.