You can check the version of perl module with something like this
which will try to load version 9999 of the module, fail, and report the version that is installed.
As for downloading/installing - the basic steps are (assuming Unix/linux)
download the package
gunzip -c package.tar.gz | tar xvf -
The packages (DBD-Sybase-1.08.tar.gz and sybperl-2.18.tar.gz) both include READMEs that explain this is a little more detail.
The main thing is to make sure that the SYBASE env. is properly positioned before running "perl Makefile.PL".