A lot of people, businesses included, have more or less decided to skip upgrading their OS to Microsoft Vista. Windows XP works for them, is well supported for foreseeable future, and many feel they can skip a generation and wait for Vista's successor, dubbed "Windows 7" to come along. Gartner Research VP Michael Silver thinks that might be a mistake, for large businesses, anyway.
...while Microsoft will support business versions of Windows for at least 10 years and Windows XP will be supported with security fixes into 2014, many software vendors won't support their products on Windows XP that long and won't support new versions of their software on older operating systems.
For Windows XP, software suppliers will probably start dropping support in early 2010, and by 2012 it will be common for software vendors not to support Windows XP for their new versions or applications.
Gartner also warned while Microsoft said it would deliver Windows 7 about three years after Vista shipped, "Microsoft's track record for shipping new versions of Windows is not good", pointing to delays with both Windows 2000 and Vista.
Microsoft is especially unlikely to rush a replacement for Vista to market if there's a large customer base hanging on 'til the last minute to upgrade their OS. They'd probably wouldn't care if they sell you a copy of Vista five minutes or five years before they come out with Windows 7. Gartner goes on to advise that if you're good at staredowns and you're a small business, maybe you could chance it.