That sounds like one of the old Keyspan PCI serial cards. I think I've still got one in a drawer somewhere.
I don't think they ever released an OS X driver for them, I'm not even sure they worked with Mac OS 9.
But I think AC was talking about the Keyspan USB serial adapters. I never used any other USB serial adapters, I've probably got 5-10 of them sitting around somewhere. I haven't needed one in quite a few years.