This is not obvious, but on the same site for the logo there is a link to obtain a certificate with a significant discount. I think I remember that it was $ 100 instead of $ 500? And this is from Verisign. I took my client through it, and obtaining a certificate became an easy part of the process :-)
Update : this page http://msdn.microsoft.com/en-us/windows/ff718579.aspx simplifies:
Submissions for Windows Logo Software Software compatible will only be accepted through Winqual. To create a Winqual account for your company (a prerequisite for creating user accounts), you must establish the identity of your company using the VeriSign certificate. There are two VeriSign certificates supported by Winqual for creating company accounts ...
Basically, you should have some kind of Verisign certificate, but it doesn't have to be code signing. You can use $ 99 just to prove that you are, and then buy your code by signing it from anyone in a PDF, which you can download from http://support.microsoft.com/kb/931125 (it appears to include Comodo). Or you can buy code signing from Verisign and cover both bases. Here you can also find a link to the offer in the first year in the amount of 99 US dollars.