Please use <CODE> ... </CODE> to surround any code or other file contents you post, as that will make it more readable and responses more likely.

This is what you posted :

The input is for example: 
http://www.ad.nl/actueel/ZZZK51QP4DC.html&May occure often & 
The output should be: 
url1=http://www.ad.nl/actueel/ZZZK51QP4DC.htmlitem1=May occure often 

And this for more lines. 
So the number must increase for the next line. 

$vervang =~ s/http/url1=http/; 
$vervang =~ s/&/item=/g; 
print $vervang; 
@buffer = $vervang; 
print @buffer; 
foreach $teller(0..15) 
{ 
  $telop{"http"} = 'url' . ($teller+1) . '=http'; 
  print $telop; 
} 
foreach $vervang(@buffer) 
{ 
  $vervang =~ s/& http/$telop/gi; 
  print $vervang; 
}
[download]

Here is my try at it (completely untested, sorry) :

  use strict;     # always do this

  my $line;      # this will contain the current line read
        # from stdin. We could also have used $_,
        # but using $line is less cryptic
  my $counter = 1;
        # This is the counter of the urlXX= string

  while (<>) {    # while we get input, we read it
    $line = $_;

    # Munge the current line into what we want
    $line =~ s!^http://!url$counter=http://!i;

    # BastardOperator made a post below that got me thinking.
    # Maybe you want it this way :
    $line =~ s!&!item=!g;

    # but maybe you want item1=bla item2=ble etc.
    # This line will do the second :
    my $itemcount = 1;
    while ($line =~ s/&/$itemcount++/e) {
      # the action is in the while statement
    }

    # and print it
    print $line;

    # and increment our counter
    $counter++;
  };
[download]

  @buffer = $vervang;
[download]

# Munge the current line into what we want
    $line =~ s!^http://!url$counter=http://!i;
    $line =~ s!&!item=!g;
[download]

I think this should be

# Munge the current line into what we want
    $line =~ s!^http://!url$counter=http://!i;
    $line =~ s!&!item$counter=!g;
[download]

Otherwise, great post

Perhaps if you would just give a few lines of input and a few lines of output, we could figure out how to achieve that, but your example data is inconsistent with the code below it. Specifically, "item=" v. "item1=".. Is the "& may occur often" bit part of the input or are you saying that that input may occur frequently?

I for one would work better in this case with 3 or 4 lines of example input and the 3 or 4 lines of resulting output, especially if it's just a few simple substitutions..