The driver you need can be found here:
http://www.digi.com/support/productdetl.jsp?pid=1415&osvid=110&tp=1&s=0
As far as installing in SCO Openserver 6, this is not done through custom but by doing "pkgadd -d /path-to-driver/40002486_b.bin
Intel motherboards had a bios bug that the "b" version driver works around. You may be seeing this bug so I'd recommend installing that instead.