Is your software compatible with Windows 7? Windows 7 Compatibility Center
will check for you.
Update your software to Win7 compatible version or install WinXP on the desktop PC seem like the easiest solutions. You can run a Win7/WinXP dual boot option to be able to use both OS. Dual Boot Installation with Windows 7 and XP
You can also see if you can find a solution using the Microsoft Application Compatibility Toolkit