FWIW: PCI-X *should* fall back to regular PCI if you can fit it in the
slot (ie. correct voltage supports so the keys line up properly). It
has for every PCI-X card I've ever used in a regular PCI slot. (FC
HBA, iSCSI HBA, SCSI HBA, GigE NICs). You just lose the 64-bit bus
option, and depending on the slot, the speed increase PCI-X gets you.
OOTH, more likely is that you didn't have the driver for Solaris 9 for
that card. Solaris 10 would offer much more compatibility all around
for options (as well as your USB question..). Or finding the proper
driver to load in the kernel for your system if it exists.
While I only see x86 systems being tested for the (few) GigE cards in this
list, if they are written properly, they'd work on SPARC too..
http://homepage2.nifty.com/mrym3/taiyodo/eng/