Brent Fulgham has put lots of work into producing a Windows Cairo port of WebKit, which doesn’t rely on Apple’s proprietary backend stuff (e.g. CoreGraphics, CoreFoundation, CFNetwork). I believe that is what you are after. The details aren’t entirely collated in one place, but there is some information in the Trac wiki and other bits are dotted around on Brent’s blog.
EDIT: Link to Brent’s project on sourceforge
EDIT 2: News of some interesting progress from Brent’s blog