Cannot install Home and Student 2007, '0' is not a valid character

* Have desktop pc with Windows XP and Office Premium 2000
* Purchased laptop with Windows 7 (has trial version of Office H&S 2007)
* Purchased Office Home and Student 2007 from Amazon (can be installed on 3
home computers)

I cannot get Home and Student software installed on either computer. When I
try, I can't get past the Product Key page. It tells me that '0' is not a
valid character in the product key. But, my product key definitely has zeros
in it. So, why can't I enter that number?

Will uninstalling the trial version on the laptop before installing the full
version solve my problem? I've read stories of people who still could not
install. So, I'm leery of trying that.

And, what about my desktop pc? There isn't a trial version on that or even
any remnants of one (I had to wipe it clean and reinstall the OS a few months
ago). It has Office 2000 Premium on it. I tried uninstalling that, rebooting,
and then installing Home and Student 2007 with no luck. I still get the
message that zeros are not valid characters.

What can I do to get my software installed and running on both of these
machines?