I found a WiX Tutorial, but it's really long-winded and seems like more than I wanted. What's the best way to get started quickly?
My end goal is nothing really complicated: an installer that installs an ISAPI filter.
I used that same tutorial a couple years ago when I needed to learn WiX. MSI (and therefore WiX) are incredibly complex, you'll need to invest some time to get it right.
If you have Visual Studio, I highly recommend getting Votive (which, I think, comes bundled in WiX v3 now). It'll set up VS to recognize the WiX XML schema and make hand-editing XML files much easier.