My 1950pro AGP had to be installed manually from device manager to work on win8 so that my be your best bet.
And also as BZ suggests you will probably save some gray hair by just getting a cheapo PCIe card.
OTOH, it's possible there is a switch on the mobo or in BIOS to determine which graphics adapter is to be used i.e. AGP vs PCIe. If the previous graphics was PCIe then that's worth looking at.
#1: Phenom II C2 955BE @ 3.6, Antec Kuhler 920, Gigabyte GA-MA790FX-DS5, Asus 5870/V2, ASUS Xonar D2X, 4 x 1gig OCZ2N1066SR2GK @800, Antec Truepower New 750, Arc Midi, Vistax64
#2: Athlon 64 X2 4200+, AGP 1950pro, Audigy 2, Asus A8V-D, 2gig ram, Enermax 465P, Antec900case. Now on Win8.1pro cat 10.2