If you are using Windows Live Messenger, then this will not be possible until the released of Messenger Plus! Live.
If you are using MSN Messenger:
In the main conversation window, type in /nick (this is the command to change your nick remotely from the chat window). after /nick, type the name that you want such as:
/nick Panic! Was Here.
Where you want the colours, highlight that area and press ctrl+k and choose the colour that you want... Once done, press the "send" key, and your name will have changed. Please also remember that the name length still applies here, it can only be 100 characters (is that right?).
To change formats (
bold,
italics,
underlined and
strikethrough, simply highlight the areas you want a different format and press ctrl+r
. This will bring up the format box.