My old Acer laptop has failed (dead motherboard). It came without setup discs. I want to extract Windows XP from the hard drive to install on a new laptop, which I'm downgrading from Vista because some software won't run. Tim Brown
I'm sure that the Windows XP that came with the Acer was "licensed with the hardware as a single integrated product and may only be used with the hardware", which is why it didn't cost you very much. You have no legal right to run it on any other machine. Even if you can get it running, you would still have to activate it. (A retail copy of Windows XP can be moved between PCs, but is absurdly expensive.)
Microsoft often provides "downgrade rights" as these can be useful to businesses. Vista Business and Ultimate can both be "downgraded". In the unlikely event that you have one of these, you will have to read your EULA (End User Licence Agreement) to check your options. However, I'm surprised if you have many programs that won't run under Vista. The ones that won't run are usually programs that operate at a low level (where Vista has changed a lot from XP) or perform non-legal operations. Examples are anti-malware programs, CD/DVD authoring programs, and games. See the Windows Vista RTM Software Compatibility List.
To get other software to run, right-click each program's .exe file, select Properties, and then click the tab marked Compatibility. Tick the box that says "Run this program in compatibility mode for" and then select the mode you want. Examples include Windows 95, Windows 2000 and Windows XP (Service Pack 2). You may also need to tick one or more boxes such as "Disable visual themes" and probably "Run this program as an administrator".
At home, all our software runs in Vista without using a compatibility mode, though some programs needed patches. I'd have doubts about both the programming competence and management capabilities of any company whose current software doesn't run under Vista. I'd look for alternatives, rather than downgrade.
