Portable does keep everything in one folder, but you lose some options just as using irc:// links. Also, you may still run into issues in Windows7 or Vista if you use Portable in c:\program files\.
The easiest thing if you want everything to work "normally" is to install to something like c:\mirc\ and to create a blank mirc.ini file or copy the one from your users folder and put it in the same folder as mirc.exe. Don't install as portable with this option. Just copy or make a blank mirc.ini and you're set. It will then only use that folder.
Note that this is the third time someone has said to do that. If you don't want our advice, why ask?
