Just because you are an administrator, doesn't mean that every application you run executes with administrative privileges. Quite the contrary, in fact - UAC (User Account Control) ensures that applications run with limited permissions by default, unless you explicitly authorise an elevation of privileges for that application.
Many applications are able to handle this and will trigger an UAC prompt; in such a case, simply approve the prompt (after you've verified that it was triggered by something you did, of course). Other applications, though, will simply complain about lack of privileges, in which case you'll have to restart the application as Administrator (right-click on .exe or shortcut and choose "Run as administrator", or hit Ctrl+Shift+Enter).
An alternative is to disable UAC completely, in which case any applications you run will execute with all the privileges that your user account has, but that's a major security risk, so be sure you understand the possible consequences before doing that. Essentially, you'd be reducing the security of your Windows 7 machine to the level of Windows XP.