You didn't mention which distribution you were using; on rpm.pbone.net I found something like 'expat-libs' and 'expat2-libs' and so on, that supposedly have that file, but mainly for SuSE only.
Have you checked if you have that file, so that it isn't just "found"?
Code:
locate libexpat.so.1
And you could also try rebuilding your rpm database, along with running ldconfig:
Code:
rpm --rebuilddb
ldconfig
and re-trying. Odd if the driver installer is asking for that file but doesn't mention where to get it from.