可以并排安装相同版本的Visual Studio的几个套件吗？

I would like to know if I can install say Visual Studio 2008 Pro and Visual Studio 2008 standard on the same machine. I have tried to install the pro (trial edition available on MSDN) after the express, and it seems to require them to be installed in the same directory. Is this specific to the express edition ?I would like to know if I can install say Visua