Unless you have the Enterprise Edition or Ultimate then a language change is not available without a complete reload of the OS using a language specific DVD. You can install LIP packs but these change the base language so the Headings are in an alternate language but they are not great. It changes the Heading Language of things like Start, Computer, My Documents and the like but as I say they are not great as most of text based things like error messages remain in the original language.Change the language from English to Spanish for Acer Aspire 5920G Laptop with Windows Vista?
If you have the Ultimate versiion of Vista, go to Windows Update and download the language pack.