Hi,
If you have the employee information in a SP list then you can add one more view with row limit to 10000 so that in future if there is large number of user then this view will display all the users (of cource <10000). then create a secondary data source for receiving data. specify XML as data source. During the creation of this secondaru data source when it ask for the XML path specify http://servername/_vti_bin/owssvr.dll?Cmd=Display&List={Your list id}&XMLDATA=TRUE&View={your view id which display all records}
You can goto settings -> list settings and from URL, you can get the listid for your SP list.
Now select "all records" view from views on the same screen and you will get list id and viewid both from the URL. copy it in notepad, edit and then put it in the above XMLpath specification.
Use this secondary datasource as a datasource for the dropdown. thus you can display all user list from SPlist to a drop down.
Bhavesh