From the MS website. To get everything on the PC in English you need to re-install Windows, but the bellow may help you a bit.
Using Multilingual User Interface:
MUI is used either in a Windows Vista deployment scenario or on a local computer when the user changes language support. The benefits of MUI are more significant in the Windows Vista deployment phase, particularly in multinational organizations.
Configuring country/region and language options
You can use the Regional and Language Options settings in Control Panel to configure input languages for user accounts. For the MUI Pack, use these settings to specify or change the default user interface language or to install or remove user interface language packs.
To change the language for non-Unicode programs
Log on as an Administrator.
In Control Panel, click Regional and Language Options.
Click the Advanced tab, and then under Language for non-Unicode programs, select the language for which the application was developed.
Limitations of language packs
Licensing requirements state that versions of the Windows Vista operating system can include only a single language, with the exception of the Windows Vista® Ultimate and the Windows Vista® Enterprise editions. For editions other than Windows Vista Ultimate and Windows Vista Enterprise, Windows will automatically remove all non-default languages from the computer after the end user completes the Windows Welcome.
After installing a language pack, you must recreate the Lang.ini file in your Windows distribution. Lang.ini specifies the languages available in a Windows image. The Lang.ini file specifies the default language to use during Windows Setup. To update the Lang.ini file, use the Intlcfg.exe tool.
In upgrade scenarios, you cannot upgrade from one language to a different language. All upgrades must be performed in the same language.
All Windows distributions are released with a preinstalled default language. This default language cannot be removed. The default language is used to generate computer security identifiers (SIDs) and language-specific directories.