I recently installed NetBSD-current (4.99.12 at the time I did this) inside Parallels Desktop for Mac. Everything went fine except for the configuration of the XFree86 shipped with the base system: I was unable to get high resolutions to work (over 1024x768 if I recall correctly), and I wanted to configure a full-screen desktop. In my specific case, this is 1440x900, the MacBook Pro's native resolution.
It turns out I had to manually add a mode line to the XF86Config file to get that resolution detected. I bet recent X.Org versions do not need this as, e.g. Fedora Core 6 works fine without manual fiddling.
Writing mode lines is not fun, but fortunately I came across an automated generator. In fact, this seems to be just a web-based frontend to the gtf tool provided by NVIDIA. So I entered the appropriate details (x = 1440, y = 900, refresh = 60), hit the Generate modeline button and got:
After that I had to make the HorizSync and VertRefresh values in my configuration file a bit wider to fulfill this mode's request and everything worked fine. Be extremely careful if you mess with synchronization values though; incorrect ones can physically damage a monitor, although I think this is not a problem for LCDs.