OK: How about this:

$ cat testMD5.pl
use strict;

foreach my $url(qw@ /index.html /about/time.html @){
        hashit($url);
}

sub hashit {
   my $url=shift;
   my @ltrs=split(//,$url);
   my $hash = 0;

   foreach my $ltr(@ltrs){
        $hash = ( $hash + ord($ltr)) %10000;
   }
   printf "%s: %0.4d\n",$url,$hash
   
}
[download]

which yields:

$ perl testMD5.pl 
/index.html: 1066
/about/time.html: 1547
[download]

Keep in mind this is hardly bullet proof. You need to also keep in mind a method to detect hash collisions and and a rehash algorithm.

This brings to mind "the old days" circa 1974 writing assemblers for 8080 microprocessors. Symbol "folding" and hashing.

UPDATE: Limiting yourself to four digits may not be very useful if you have a lot of pages that you are trying to index into your database. The wider your hash is the less likely there will be hash collisions.