I want to replace the 'client' field text box in fogbugz when you edit a case to be a drop down instead populated from a separate web service that will keep the client options up to date in our fogbugz. Is this possible? Will the choice they select in the drop down be able to save the same way it would if they had typed it into the text box?
If you are on Windows, email us at http://contact.fogcreek.com and get on the FogBugz 7 beta which has the ability to do this with plugins (instead of GM) or even, just with a custom field.
An off-the-cuff answer:
Yes. For a first pass, you can implement it by creating the drop-down list on the side, populating it with a GM_xmlHttpRequest, and adding a "onchange" action listener to the drop-down list, which will populate the textfield with the relevant information from the drop-down. This ensures that fogbugz sees exactly what it wants, in exactly the way it wants to see it.