Screen shots are your friend.
Looks like you are running a "trident video accelerator 9440(pci slot enabled)(1 mb)" and have a "ati 3d rage pro 2x agp(agp slot but disabled)" So you have two graphics cards. Now I do not know which is the more powerful of the two or if you can get a more powerful card. But you can only run ONE CARD at a time. If you look for a better card then you need one which has the correct AGP support for your slot, probably AGP X2 or maybe AGP X4.
I can not tell what your mobo is from the information given. Mine is a Asus K8N-E Deluxe, if you can find a name something like that then you can find out more specific information on what cards your mobo supports at the Asus home site. Depending on what youir mobo supports you will be able to play some of the older games and get good quality video playback I'm sure.
You should be able to overclock as some of those older cpus clocked really well btu you would need to read up on how to do it. Flying by the seat of your pants stuff that is for surebut can give some great results.