From MetaQuotes' MT4 User Guide:
The Client Terminal can operate under Microsoft Windows XP/2003/Vista/2008/7. A processor that supports SSE2 instruction sets is required for operating as well. Other hardware requirements are limited with software ones.
Just because there are some UAC issues for some users doesn't necessarily mean that MT4 isn't compatible with Windows 7.
This is not true.
Please watch your language.
It works fine under UAC on Vista. I installed in ProgramFiles, I run a user level account. UAC actually protects against automatic live updates. UAC asks my permission and requires an administrator password before allowing MT4 (or any other program) to recieve an automatic update.
UAC does what it is supposed to do, it helps to protects the original installation from unauthorized modification or interference.
If you install outside of program files or turn off UAC or run your computer as an administrator all the time you are basically running a very unsecure environment leaving your applications open to interference by reletively simple malicious code, it is like leaving your car parked outside the garage with the doors unlocked and the keys on the dash.
That is not to say if you put it in the garage and lock it all up it can't still be stolen, it just makes it a lot more difficult.