You can edit the source in any text editor. You'll need flex sdk and compiler to generate the swf based on the source code.
http://opensource.adobe.com/wiki/display/flexsdk/Flex+4
Thank's very much. It was very usefull. By the way I found there is a perfect readme file in the krpano Google Maps Plugin:
-----------------------------------------------------------------------------
- to compile the krpano Google Maps plugin the free Adobe Flex SDK
and the Google Maps AS3 API are needed.
- the version 1.16 of the Google Maps AS3 API library is included (map_1_16.swc)
if needed get newer versions here:
http://code.google.com/apis/maps/documentation/flash/
- get here the latest version of the Flex SDK:
http://opensource.adobe.com/wiki/display/flexsdk/
- extract it to any place (e.g. "c:\flex_sdk_4")
- set the path to its "bin" folder, e.g:
set PATH=E:\downloads\flex_sdk_4\bin
- then compile the plugin with this command:
mxmlc -compiler.optimize=true -library-path+=map_1_16.swc -static-link-runtime-shared-libraries=true googlemaps.as
-----------------------------------------------------------------------------
Just remeber to update "set PATH=E:\downloads\flex_sdk_4\bin" to the path you extracted flex_sdk_4 to.