You may wish to look at either CGI::Session or (if you're going to be using mod_perl) Apache::Session. They are two of the best ways I know of for working with sessions.

You didn't ask about this, but you may wish to avoid "transforming" your ASP code to Perl. Writing an identical looking site with similar features is one thing, but when you try line-by-line conversions (which is what I gathered from "transform") from one language to another (especially with Perl) you'll often times create a lot of headaches for yourself. Learn to use Perl's features instead of looking for ways to recreate ASPs features. You'll find yourself extremely impressed by the power and simplicity Perl will provide you :)

Cheers!
MrCromeDome