Are you refering to ''online'' music such as a music share or internet radio. If so, the buffer might be set too low. The only player I am familiar with is WMP. In WMP go to Tools > Options > Performance > under Network buffering select Buffer > set to 60 seconds > Apply > OK. I don't think it will go above 60 seconds.
Hope this is of some help.
I have a Dell Dimension E310 Pentium 4 with 2.8 GHz and 504 Ram. When I open up songs or videos they do not play all the way through. It will stop and start until I end up just closing it down. I also am running sorta sluggish.