Why do you want to change? The file is very simple, a database seems overkill. Do you need support for concurrency? Is the file getting BIG? Something else?!

There are many lightweight databases around. You might want to give CPAN or sourceforge a look.

Personally I would probably try my luck with MySQL. maybe not so lightweighted but a lot lighter then beasts like Oracle, Sybase, MSSQL, Progress etc. etc. Installation and administration is straightforward, i.e. you don't have to be a DBA.

Hope this helps