Office 2K verus Office 2003

Hello –
I have both Office 2k & Office 2003 installed on my computer. I teach 2003 for clients, but prefer to work in 2000. With both installed, when I double-click a file it automatically opens in 2003. Is there a way to have the files open in 2000 instead without having to open the program and then open the file. I tried to r/c and go to Open with, but the only option is 2003 even though I installed 2003 in a separate dircectory than the default, microsoft office. Thanks for your help.