What that thread likely was saying was that someone necroposted a really old thread that was resolved and was saying that they had a problem. For help topics, you want to create a new topic in
the help forum and state your problem.
Usually you wouldn't want to install osu! in some place like Program Files because files need to be edited all the time, and running osu! constantly with administrative privileges is a bit annoying.
Alternatively, osu! is very portable. You should be able to easily play osu! on an account without admin privileges (e.g. a student account on a school computer) by just copying your osu! folder into a USB stick.
Just a note... I'm
assuming this is what you mean. If this doesn't answer your question, make a topic in
here about your problem.