My regex was a bit different. find [URL..blah] or [/URL..blah] and delete them with substitution.

#!/usr/bin/perl -w
use strict;

my $example = '[URL=http://img207.imageshack.us/my.php?image=dsc03598v
+t7.jpg][IMG]http://img207.imageshack.us/img207/2964/dsc03598vt7.jpg[/
+IMG][/URL]';

print "$example \n";
$example =~ s/\[\/*URL.*?\]//g;
print $example;

#prints
[URL=http://img207.imageshack.us/my.php?image=dsc03598vt7.jpg][IMG]htt
+p://img207.imageshack.us/img207/2964/dsc03598vt7.jpg[/IMG][/URL] 

[IMG]http://img207.imageshack.us/img207/2964/dsc03598vt7.jpg[/IMG]
[download]

Update:I recommend Jeffrey Friedl's "Mastering Regular Expressions". This a "classic". But I figure this like nuclear weapons! The vast majority of regex problems can be solved by shooting the problem 1x or 2x or maybe even 3x with simplex regex'es in a sequence. Also I've found that the performance can be just as fast as a single complex regex (and sometimes faster)!