You can use the CGI module to access such parameters e.g.

use CGI;
my $query = CGI->new;
my $id = $query->param('id');
[download]

or

use CGI qw/:standard/;
my $id = param('id');
[download]

Have you read ovid's tutorial on Web Programming Using Perl?

update: I've assumed you'll be using a CGI script in which case you'd typically pass the parameter like:

http://www.perlmonks.org/cgi-bin/test.cgi?id=1
[download]