Some time ago I talked about the program "FetchXML builder" to build FetchXML queries: http://ronaldlemmen.blogspot.com/2006/09/fetchxml-builder.html, but take a look at the next solution.
You can just open the Advanced find page and build the query as you like. Then run the query to see if it returns the data as you wish it should. If you are satisfied with the results and you want to know what query was sent into the CRM Framework, then press F11 to get the address bar and enter this script and press enter.
If you get a warning about leaving the page, just press 'ok' and then the query which is sent to the framework opens up in a popup. Unfortunately you cannot select the text to copy and paste. But with Windows XP and Windows Server 2003 you can copy all text on the popup by clicking somewhere on the popup (not on the button "OK" ofcourse) and pressing ctrl+c. Now in notepad you can paste the text of the FetchXML.