Dave, Mushroomboy: I understood exactly what OP wrote. If he does as I told, his issue is solved and the system language is completely changed. Also in login, logout and welcome screens.
Multimolti, it is of course up to you who you believe, but I know what I am talking about. Just do as I told you above in my earlier post.
Language pack changes the language of Vista or Win7 completely. I've been using Windows in four different languages since it is been possible, from early beta versions of Vista in 2005. My main system today is a German 7 Ultimate with English, Finnish and Swedish language packs (see my attached login screen) and I have never seen one single word of German here except when logging in to a German account. The system is completely English when I log in to my work account, or completely Finnish when I log in to my private account, completely Swedish when I sometimes have to login to Swedish account.
When installing this German 7 Ultimate, I first created the main (and only administrative) account (Kari (Work) in the image). Then I installed the language packs I need, changed my main account's language to English and did as described in my post above before creating any additional accounts. As the result, all additional accounts I create have English as default and the logon and welcome screens are in English.