I found a very interesting page on D-Link's website: <http://support.dlink.com/faq/view.asp?prod_id=487>
wherein a clue may perhaps be found. It seems that Revisions A, B and C of this board (the DFE-530TX+) do indeed use rtl8139.o from the standard distribution. However: For Rev. D1 and D2 of this card, the web page says, quite specifically and in no uncertain terms: "DFE-530TX+ revision D1 and D2 must have the driver compiled from the floppy." Indeed. This evening I gave up on this debian installation and decided to rebuild it from scratch. Interestingly enough, the rtl18139 driver fails to install even during the initial OS setup. This would explain a lot. It seems I either need to get a less-exotic NIC, or deal with building this module from source. rafe b.