here is the method i use for one-off affiliate links. create a little php file, say innocuous.php, which looks something like the following :
PHP Code:
<?php
$redirect_url = 'http://some/url/with/an/affiliate/id/';
header( "Location: {$redirect_url}" );
?>
then just direct people to innocuous.php and they will end up on the appropriate sales page. this is a lot easier than writing HTML files, i think.
of course, the file has to go into a directory that can handle PHP scripts, but most document roots handle PHP without any problem.