After months of limited testing, Microsoft late Wednesday made a beta version of Windows Vista publicly available for download.

The company kicked off what it called its "Customer Preview Program," a testing period in which the software maker hopes millions of tech enthusiasts will kick the tires on the new operating system.

"Microsoft today kicked off the Windows Vista Customer Preview Program (CPP), providing the broadest access yet to pre-release test versions of Windows Vista," the company said in a statement. Microsoft is aiming to wrap up testing and development of Vista later this year in hopes of a broad launch in January. The company released Beta 2 last month to a more limited group of testers and had promised the broader test would come shortly.

The software maker is still cautioning that Vista is not ready for the average consumer, pitching the CPP as suited for developers and tech workers, as well as hard-core enthusiasts who don't mind a few bugs and have a spare machine for testing. Microsoft also recommends those interested in the CPP run its recently released adviser tool, which helps detect how Vista-ready a PC is.

People can either download the software from Microsoft's Web site or pay a small fee to get it on DVD.

Although Microsoft is looking for millions of testers, it has said it may cap the test program at some point.