Quit a setup if a required is not present

Hello,

First, sorry for my english.

I used MUI.

!insertmacro MUI_PAGE_WELCOME
Page custom "installDrive" ""
Page custom "connectorInfo" "ifConnectorExists"
Page custom "databaseInfo" "databaseInfoLeave"
!insertmacro MUI_PAGE_INSTFILES
!insertmacro MUI_PAGE_FINISH 

For my setup, I test just after the welcome page if the MSXML4 parser is present.
If not, I want to stop the setup so go to the finish page.

And I don't know how can I do that, I don't know where I can do the test (perhaps in page "installDrive" and I abort each page if a variable = 1 for example) and how change the text in the finish page (the text is not the same after a good setup or after I know the parser is not present).
I tried with a custom page, but I prefer the finish page look.

This kind of tests are usually done in .onInit with a simple message box to note failure.