As of right now, August 27, 2010, the only app that can play from a media server on android is uMediaPlayer and based on the reviews, it does not work most of the time. Why there are no clients but umpteen million servers, I do not know.
As an alternative, you can use TVersity and then use the flash interface they made through your phone browser (Froyo+ only, requires flash support). This is much easier to do if you have a trackball phone, as using the flash interface with a touch screen is difficult at best. You can also try Orb, but for video it does a poor job compared to TVersity through browser.