The system sounds like a pretty good system for what you use it for. If I was going to build you a new one and keep the budget I would build you an AMD 5000+ Black Edition or better on a Gigabyte GA-MA69GM-S2H, or GA-M57SLI-S4 board with 2GB of DDR2 800. THen we would pick out a mid level videocard. What power supply are you running now? That may need an upgrade also. This would work just perfect for you as it does for me.
I would ditch the AGP and build the new setup. Plus you can OC the 5000+ BE by just upping the multiplier and not overclocking anything else. Mine is currently at 3.0GHZ.
1993 Bonneville SC SSE With Supercharged Badges, Black and Gold, CAI, 180T, TR-55'*, 2.2 Pulley, Jet Stage 2 Chip, Ceramic coated PEM'*, Magnaflow, Flowmaster 80, Megs Tips.
1995 SLE (Wifes), White and Gold, CAI, APN, Magnaflow, otherwise stock.
1966 Ford Ranchero, 312ci 60 over block decked, GT40P heads Milled, RPM Air Gap intake, Holley 600, MSD Billet Dist., 6A Box, FlowTech Shorties, C-4 W/Shiftkit, 8" 4.11