I think a 1.8 Ghz Duron is going to outperform a 500 Mhz chip, James1980!
1. You need a gfx card with more memory, 8MB is insufficient. Geforce 5200 FX is a good value card at the moment if you can stretch to around $70. This would get you a card with 128 MB of memory and shader support.
2. Check your BIOS AGP settings, that the speed matches the card.
Set the gfx memory shadowing to 8 MB to match the card.
3. Switch off any "smart" software monitoring of the graphics performance if you have any installed.
4. DB is going to select your primary card, but you can force it to select whichever card you like, check the help files for enumerating and selecting devices.