Amy, Tommy Boy is right though.
If your website is accessible both as
http://vbulletin.com and
http://www.vbulletin.com, then set the cookie domain to .vbulletin.com in the Admin Control Panel Options page.
This has NOTHING with users being computer illiterate, it's got to do with Admins not doing it right. It doens't make sense to me that you as an admin would prefer to install a hack rather than set the option that already exists in vB correctly.