Uninstall is not availible for DX9.
Is it a new card?
Ti4600 only suports DX8x but should work fine with DX9 dont think that it makes a difference performance wise just added graphic and sound enhancements.
have you got your mobo AGP drivers installed?
if not agp will work in PCI mode. is your AGP set to X4 in bois X8 if your mobo suports it?
Cant remember much about win 98 but think updating drivers may help a little, but think that there is an underlying problem. doubt it is caused by DX9