The current (R5.03) version of Be’s RealPlayer has very limited network settings. Although it would be nice to be able to set how long to buffer before playing, you can’t.
A workaround is to: start the clip and start it playing. Then, as it begins buffering, pause it. Keep it paused and it will keep downloading the clip, buffering more and more. You can also do this again after you’ve been listening for a while.
Note : This is only effective for non-live feeds.