A few tips:

• You may want to have a look at Mastering Regular Expressions.
• Komodo, ActiveState's Perl/Python/XSLT/whatnot editor has facilities to play around with regular expressions, it might be nice to learn by experimenting.
• Along the same line, the YAPE::Regex::Explain module on CPAN "explains" what a given regex does.
• There are several entries on regexs in the Tutorials section of this site.
• There's of course also perlre, but that you problably know.

This should get you started I hope, -gjb-