I initially has VS 2003 and then installed VS 2005, no problems. However, I had to re-install my operating system and because I had deadlines, when I got back up and running, I just installed VS 2005 because most of my work was with that. But recently, I had a program that wouldn't convert from vs 2003 to vs 2005, so I needed to look at it in 2003. So I went back and installed VS 2003. Nothing really bad happened, except when I doubled on a VS 2005 solution, it tries to open it in VS 2003 and I get an error. I have to right click on the solution and select Microsoft Visual Studio Version Selector which then opens the solution in VS 2005. I haven't found a better solution.