im not sure if my board is the exact same as yours (the system is a compaq presario 7462 so i dont know the board model but it was made by via) but i have two dimms, no agp (which sucks) 4 usb, and 4 pci. i replaced the crappy trident card with a tnt2-m64, but pny now (who made my video card) also have a geforce 2 pci. if you can find the geforce 2, i'd get that over the tnt2 cause of its fsaa abilities and superior ability in opengl.but if not, then i would just get the tnt2. if i remember right, both should be around $70 USD, but the price may be different now.
(EDIT: im not sure, but if you have the same board as me when you replace the trident card, you should be able to take 6MB away from it changing the amount in the bios or disable it completely, which gives you an extra 8MB of memory and it will automatically add it to your cpu's total amount of memory)