Odds are that you've been sold an illegal and re-re-re-re-used license number - kind of like selling the Brooklyn Bridge over and over. Since they didn't actually have to send you anything like a CD or manual, their costs were zero. As you've discovered, you've bought a 7+ year old version, that is now 7 versions back. It's not supported on Windows Vista or Windows 7 and it doesn't support Office 2007.
Does the download link work? I ask because I don't believe there are any legitimate download sites anymore for such an old version.
Whether or not you need a previous version is somewhat moot at this point.
I would recommend discarding it, and buying ACT! 2010 - the real thing, including a box and DVD, from an online or a brick-and-morter retailer.
ACT! 6 didn't require registration and the web site for registration was shut down a long time ago. To amplify what Kevin had to say. the copy you have is likely a pirate copy and as such is illegal. I've also heard many horror stories regarding so called OEM copies of software. Because they are pirate copies, they are often used as trogans for viruses and other malware. My personal advice for what it's worth, write off the $40 you paid as a lesson and, if you have access to Costco, check for ACT! 2010 there. I understand they are selling ACT! 2010 standard for little more than you paid for your antique copy of the ACT! program
