I don't know anything about PCX format itself, but
would try out portable bitmap tools:
pcxtoppm file.pcx | pnmtorast > file.rs
for sun raster, importable by r.in.sunrast, or
pcstoppm file.pcx | pnmtotiff > file.tif
for tiff, importable by r.tiff
If you try it and it works, let me know!
John Mackenzie
U. of Delaware (and URI alum)