I've never even paid attention to the PCI revisions, they're backwards compatible, so if it'll fit the keying of the slot, it should work fine.
I'm not sure what they mean by 32/64 bit, since that's just a regular 32-bit PCI card, not 64-bit. As for the 66mhz, it's a bit complicated, but basically, 64-bit PCI can come in 33, 66, 100, or 133mhz speeds, and it will always fall back to the lowest speed device installed. Like, a 133mhz bus would fall back to 33mhz if you installed a bog-standard PCI card. So, a 66mhz card would assure that the bus would at least run at 66mhz. Presumably, anyway... I'm not entirely convinced that Rosewill is actually a 66mhz card.
And anyway, that sort of stuff only really matters in higher-end server and workstation hardware... everything else just uses standard 32-bit/33mhz PCI. So I don't really see the selling point on that NIC... it's not like the high-end workstation market is going to be looking for a $15 off-brand NIC.
In any case, I wouldn't buy that thing. Look at this place, they've got Adaptec NICs for $3, and 3Com 905's for $6.