If you're shopping for a new PC, you may want to wait until Friday. That's when Microsoft and computer makers could start giving coupons for a free copy of Windows 7 to people who buy a new Windows Vista PC.

The coupons are intended to encourage people to keep buying PCs instead of holding off until a new operating system is released. It may be a crucial incentive this time around, since Vista has such a bad reputation and Windows 7 will be widely available on Oct. 22. (I've asked Microsoft for confirmation and will update when I hear back. UPDATE: I heard back but they're holding comment/info until Thursday morning)

It's also a good deal, because it gives buyers two operating systems for the price of one. (Assuming the older system will continue to have value after the newer one's released ...)

Microsoft hasn't said much yet about the coupons, but enthusiast blog Tech ARP has been posting what looks like authentic details of the program, dubbed the "Windows 7 Upgrade Option."

If the details are correct, computer makers may offer the coupons between June 26 and Jan. 31. Within that timeframe, they can decide how long to offer the deal. Customers would get Windows 7 on Oct. 22 at the earliest, and April 20 at the latest.

The coupons will offer the same tier of operating system -- buyers of Vista Premium could get Windows 7 Premium, Vista Ultimate buyers would get Windows 7 Ultimate, and Vista Business buyers would get Windows 7 Business. Vista Basic systems won't be eligible, the report said.

If you're buying a Mac and wondering about upgrading to the "Snow Leopard" operating system coming in September, Apple plans to provide single copies for $29 and five-packs for $49.