Java does not provide an interface for interaction with Power-Point as standard. There may be third party libraries that will facilitate this. I guess it depends on what you mean by interact.

You can certainly read (and write!!) powerpoint files. They are after all a series of bytes just like any other file ;-). Whether or not you can do anything with the data once you have read it into memory depends on your knowledge of the file's structure. Again there may be third-party APIs that will take some of the pain away. What do you mean by 'transfer .ppt files through java from one client to another'?

Capturing the screen's contents is an operating-system dependant action and as such is not supported by Java. The only way to do it would be via the JNI.

Regards.