I’ve been using the beta of Microsoft’s Windows Home Server, and I’m a fan. But Microsoft is making one big mistake with it: It won’t sell the software to people like you and me. It’ll only go to systems makers. Microsoft is missing a big opportunity here.

I’ve installed Windows Home Server by reformatting a Windows XP I have laying around. It’s got a 300 GB hard disk, 2 GB of RAM and a fast enough processor to handle Home Server. I’m using it to back up files, serve as a central data repository for a number of PCs on my network, and to share files. I’m using it for exactly what Microsoft says Windows Home Server should be used for.

I’m not alone. I know plenty of people with spare PCs that are a few years old that would be perfect for Home Server.

Microsoft, though, won’t sell us Home Server. Instead, we’ll be forced to buy an an entirely new system with Home Server installed on it. All we need is the software, though; there’s no need to buy the hardware.

But Microsoft says you’ll only be able to buy entire systems, not the server software itself, unless you’re a system maker. I’m guessing that there will be gray-market copies floating around, because Microsoft has said it will sell to OEMs, who can then build their own boxes. Don’t be surprised if somehow that OEM software gets out into the market.

I’m not sure why Microsoft decided not to sell to end users. They may be frightened away by the potential support nightmare it could cause. Or they may not want to compete directly with the system makers to whom they’re selling the software.

Whatever the reason, though, it’s a mistake. There’s a big market out there for people with older systems who would flock to buying this software — but they’ll balk at forking out for an entire new system.