If you bought the "Ultimate" license level of Windows 7, you'd get access to the built-in Windows XP virtual machine. You could run your older software under that without any problem, as just another window inside Windows 7.
Of course, you'd still be using XP, but it would work, and you wouldn't need another computer to do it. So far, I've never found an XP app that I couldn't get to run under the W7 XP VM.