How can I install a file If the window said I must use an administrator/power user account. Any Idea to share?

no, you can't do it. That's why companies have IT departments, to control things like that

you have to log off first, then login into the other sign in name

hmmm idk,lol

All kidding aside, there are legal issues that your company can be exposed to, not saying you are going to do anything illegal, but limewire has a reputation for certain kind of activity. If your company has an IT department it probably also has a Security department and even if you were successful in downloading limewire, I wouldn't be surprised if your IP address is flagged when or even if you are able to connect and it isn't blocked. Did you have to sign or go through some kind of computer usage orientation? Think carefully whether or not it is worth it.

Better get permission. Let the expert. That's their job

hmmm........try using a proxy blocker site..im not 2 sure what else to do tho-sry. :[

I don't know if it's possible. An administrator account on my computer-- which isn't a company computer-- can be used by entering Safe Mode, but I don't know if you can do that without full administrative rights. Your guess is as good as anyone's.

This is why company admins don't give you admin rights. Limewire and similar services do leave a machine vulnerable to bugs of various kinds. In a serious network anyone with admin rights could cause the problem to spread round the network in about 10 minutes, the cost to the company could be crippling. Many of the companies I manage IT for have strict (instant dismissal without references) rules against installing unauthorised software.