, RichardD3 wrote

I wouldn't be too upset if we couldn't use 4.5 on XP/2003, so long as it wasn't an in-place upgrade. As it stands, we can either buy into the multi-targeting lie and write 4.0 code that won't work on a computer with 4.0 on it, or ignore 4.5/VS2012 and write 4.0 code that won't work on a computer with 4.5 on it.

Install a VM with only 4.0 on it and use remote debugging. It'll need to be a Win7 VM, since remote debugging isn't supported on XP in VS2012 but it'll still allow you to test under the conditions you would have previously (in fact marginally better since your VM can be free of any apps you normally have installed on your PC that might cause conflicts).