While most businesses have soundly rejected Vista and are tenaciously hanging on to Windows XP until Microsoft comes out with a better operating system, the day of reckoning is approaching. The reason: Microsoft drove another stake in XP in April, when it officially ended "mainstream support" for the operating system. This means your warranty on XP is void. It also means that if you want support on XP other than basic patches or basic security upgrades, you'll have to pay Microsoft under a separate, "extended support" agreement.
Having an unusual problem with XP that you need resolved? That'll cost you. Need to add a new device to your system that isn't currently supported by XP? You'll have to pony up for that, too. Even worse, Microsoft may return the bad news that XP will never support a new device or new software application you've recently added.