Only on PDAs which run PocketPC (also known as Windows CE). Don't really know where you're based. In UK, there is something called XDA II (and all its variants) sold by O2.
I think Sprint and HP iPAQs also use PocketPC and probably can run Excel and Powerpoint as well. The XDA has a powerpoint viewer which may not be the same as actually running powerpoint.
I think Sony Ericsson use Symbian so they probably won't support it.