Thought of using DBD::Sybase,is it necessary to install 'sybperl'.

No. In fact, if you are going the DBD::Sybase way, you don't need sybperl at all. sybperl is useful if you want to use the full power of the Sybase specific interface (DBlib or CTlib). For instance, if you're doing your prototyping in Perl, but your final product will be written in C, you may go for sybperl instead. Or you may already be quite familiar with the Sybase API - another reason to use sybperl.

OTOH, if your goal is to be able to switch databases, the DBI/DBD::Sybase is a first, small step. You'd still need to be careful when writing SQL code though - it's quite easy to write SQL code that's specific for the current database.