Help with variables from user input

I’m creating a simple flash movie that will allow me to setup an aim away message from the desktop or merely a web page, the code used is as follows:
aim:goaway?message=Message+Here+Go+to+aimisland.com
As you can see there is a + after every word and the text is after Message+.
I need to know how to get text which is entered into a text box to be inserted into the above code to complete the link. Thanks in advance