It should be okay if you upgrade. Try without the IDE BusMaster first, and then try it if all goes well with the INF and AGP portion of the VIA 4in1's. That's what I have found to work best for me.
Here's what I do (I run W2K) for a fresh install. I first install a registry file from AMD to prevent AGP crashes, then I install the Microsoft AGP patch for W2K. If you use Win9x you don't need to worry about that. Then, I install the VIA drivers, without the IDE BusMaster. From there, I install the video card drivers, then sound card, etc. After that all is done, and if I'm having problems with my IDE controller I then install the busmaster drivers. Some people might say to install the VIA busmaster drivers before video, etc, but I actually like my system without them - because for some reason DMA is enabled. I have a KT7-RAID. Hope that helps.