Early Thursday, Microsoft opened the doors to all comers who would like to test Windows Vista Release Candidate 1 (RC1).

Testers can choose to download the 2.52GB Windows Vista installer, or request a DVD that will be sent in the mail.

Before Thursday, only previously registered members of the Microsoft's Customer Preview Program (CPP) - the 1.5 million people who accessed Vista Beta 1 in the same fashion earlier this year - were given access to RC1. Although Microsoft hasn't officially announced the number of new CPP registrants it will allow for RC1, some Microsoft executives had previously estimated that the number would reach an additional 1.5 million testers.

Those who request the DVD to be mailed to them will be required to sign in with a Microsoft PassPort (not called Windows Live) email address, answer some demographic questions and pay $5 in the US. Delivery will take two to four weeks.