Look at the code in sys/arch/i386/pci/pchb.c which matches, attaches,
and probes a secondary PCI bus behind an Intel 450GX controller.

I suspect the Compaq system has a similar bridge chip which should
likewise be probed.  If you can get the documentation, pchb.c is
probably the right place to put the driver code.

-- 
==John Kohl <jtk@kolvir.arlington.ma.us>, <john_kohl@alum.mit.edu>
Singing in the Boston Pops' Holiday Pops chorus, Dec 18 @ 7:30pm,
Dec 20 @ 11am, Dec 21 @ 3pm.  http://www.bso.org/pops/holiday/