i don't have a computer with that chipset nearby, but, I would suggest running the latest broadcom drivers as you're doing I assume. if you don't see an option in the device configuration page to turn on vlan tagging, I'd say you're out of look (look in the device configuration options, not in the advanded suite).
FYI, my intel and realtek chipsets nearby support this feature and all are enabled directly from the driver/device config page -- no optional proset software needed ;p
good luck -- worst case buy a pcmcia nic -- you can get a base1000 one from newegg (realtek chipset) for under $20
hmm ... maybe I'm misremembering or maybe it's different for the pro1000s ... either way, I'll check my intel card at home tonight (not that it really helps you).
and i'm out of my league here, having never actually setup a vlan (although if I ever find a cheap managed gigabit switch on ebay I might consider).