You probably want the 386 UP driver. A 686 kernel is optimised for a 686-class cpu and, as far as I know, the default Red Hat installation is always i386. A kernel built for i386 will run on anything higher than that, but an i686 kernel won't run on a 386.
On the other hand, the safe bet is to get the source rpm and build the driver from that. You'll need to do that anyway if you ever want to build your own kernel.