If libsybdb.so exists on your system (usually in $SYBASE/OCS-XY_Z/lib where XY_Z is 12_5 or 15_0) then the most likely problem is that your LD_LIBRARY_PATH isn't set correctly. The easiest way of setting your environment correctly is to source the SYBASE.sh (or SYBASE.csh) file located in the root directory of the Sybase install.

Michael