Apparently SysWOW64 redirection works differently on Vista x64? Using x64.nsh (it should really be called WOW64) instead of my Architecture plugin (which was accidentally a big debug dll).
Detect previous installations.
Only show properties to set compatibility mode on Vista and higher.
Show properties to set compatibility mode!
Oh, good I don't have to write that plugin.
Oops!
Multi user stuffs!
Rough start.
Stuff.
...