The Windows 95 VXD driver works fine on 98, whereas Via uses a .sys driver in the default installation that doesn't allow AGP acceleration. Choose the AGP 2.0 3.0 Compatible Driver if that's what your board has. If your motherboard has a 4X slot, that's the one. If only a 2X slot, you can use either driver but the plain Jane one without the 2.0, 3.0 support has better compatibility with older motherboards.
Eck (and anyone else!), what's your opinion on using this Win95 VXD driver with an AGP 3.0-compliant 8x slot? The VIA board I have has a KT600 chipset, and the card I'll use with it is an NVidia GeForce FX 5500 (256 MB), probably with MDGx's unofficial NVidia drivers.