Been pulling my hair to find an way to open up a .csproj file in the Visual Studio 2005 IDE. After lots of right-clicking and dragging-and-dropping I gave up and googled it. The answer was on the MSBuild Team Blog all the time. Turns out it's as easy as this:
- Right click the project and select Unload
- Right click the (now grayed out) project and select Edit
Works splendidly!