How do I change language of all the text on my computer?

My start menu and every message is in a different language, I need it to say ';starting windows'; and ';shut down'; in english.How do I change language of all the text on my computer?
I think you will need to reinstall the operating system using the Operating System CD (if you have it).How do I change language of all the text on my computer?
XP: Click Start,Control Panel, then on Date, Time, Language, and Regional Options, and then click Regional and Language Options.



Vista: Search Regional and Language Options, Then change format to english.