Help please!How to restore a program(MS2003) I just removed?

I removed my Microsoft 2003 standard edition and wanted to install my 2000 professional edition since the 2003 is only for me to try it for 3 months but the 2000 edition is mine. However, my HP notebook won't let me install the 2000 edition so I'm trying to get the 2003 back. Do you know where on the computer to get it back? I used Add/Remove program from the control panel to remove it. Thanks a lot for your help.