I'm getting to grips with DBI too. IMHO, DBI is not particularly difficult, but if like me, you have to do a MySQL install and database administration, as well as coding your app - well than can make things more complicated and time-consuming than using your standard module. So unless MySQL is setup for you, I recommend relaxing with the O'Reilly MySQL and mSQL. It's really useful from a MySQL point of view, which IMHO is half the battle.
As to DBI, I found another O'Reilly Programming the Perl DBI useful. It does take about 3 chapters to get to discuss DBI (the first few chapters are a general introducion to not-relational database persistance in Perl, which, while off-the-point, are pretty useful in themselves. I'm biased 'cos I love books - also Alligator Descartes and Tim Bunce deserve all the book-royalties they can get for providing such a wonderful module.