I know this is common around the internet, but there still seems to be some confusion about this topic, so I figured I would add to it ;)

1. You *can* compile to 1.0 compatible (and mono compatible I would assume) code from VS 2005.
2. You *can not* use any 2.0 specific language features when doing so (partial classes etc).
3. Your project and solution files will be stored in 2005  format, so you wont be able to open them in 2003 without alot of stuff going on (proj files for both IDEs or something crazy like that).

Other than that, its just a matter of doing it. You can't (I don't believe) change the framework on the solution level. You do it per project, to each project in your solution. Or at least each one you want to run in the 1.0 framework, in case for some reason you want some each way.

Right click the project, choose Properties, choose the Build option, choose Advanced. You will see a drop down beside Language Version. Change that to “ISO-1”. Rinse and repeat for the remaining projects. It *will* complain and not compile if you use a post 1.0 language feature.