At work, we use all Windows, so we use SQL Server 2000, with Win32::ODBC. I've also used mySql with DBI on Windows and Linux. With 100,000 rows, either of these will probably work pretty well for you. Using mySql will obviously be more cost effective.

I've never pushed mySql to the limit, so I'm not sure how big a DB has to be to hinder performance. I've used SQL Server with table that held 1-2 million rows, and it was still relatively fast.

I'm normally a Linux user, so I would personally use mySql with DBI.