The chipset does not make the modem. As i said for a example, i have a Biostar mother board, but i have a nvidia chipset. Does that make it a nVidia mother board? No. It is still Biostar's.
I cant say if they are or not. Cause it can technically fall under what is deemed Vista Compatible. Maybe Vista does have drivers for it. I dont know. I cant say. This is why there was a major lawsuit over that term. Cause it is unclear.
I cant say anything for or against the ebay listing just like i cant say anything for or against the card. I dont have enough information to make any kind of statement as such. There is nothing in the listing that can help find drivers as they only list generic information. Which basically can cover just about any modem made from 1996 on. Back around the time when V.92 standard was finished and Modems came compatible with it.
There is nothing myself or anyone here is going to be able to do to help. If you are lucky you can run Belarc Advisor or SiSandra Software to get some information about the card. But as i previously stated, you are much better off going to WalMart. the statement is true "You get what you pay for". It was a cheap modem and as such you haev had nothing but issues with it.
Get one from Walmart where you have more documentation, drivers and at least a make and model with a chance to return it. That is all myself or anyone can suggest.