Refer to the how-to.
The Display language section will only be visible if you have already installed a LIP or if your edition of Windows supports MUI. MUI packs are only available in Windows Vista Ultimate and Windows Vista Enterprise.
Also see the How do I get additional language files? document.
If your version is not Ultimate/Enterprise, you will have to either purchase it or purchase another version of Windows Vista in English language and perform a clean installation. That is because there is no English LIP available for the Windows Vista which comes in other Languages.
However, if you Google, you can find sites with links to the English LIP (as it's extremely hard to find the official LIP links of the Microsoft site).
This one is probably an English LIP as stated in one blog. However, there are comments that it's not a LIP, but a MUI and doesn't install on the non Ultimate Windows version:
Are you really sure that those listed files not are for Ultimate only? I mean, if I install one, it says it is MUI pack, not LIP.
Anyway, you can try if it works for you.