The KDE desktop, by default, includes system sounds such as a specific sound when a new window is open or closed. These sounds may interfer with xmms or any other audio application. Also if you use a program which uses a diiferent sound system, such as esd, then the arts sound system may then not be active to produce sound for a different audio program which uses arts.

By default the arts sound system server is started with each KDE login. A way to check to see if it is running is to run a program called KDE Sysetm Guard. It is program used to monitor which programs are running. Click the process table table on the top of the page. Check to see if there is an entry for artsd or an entry for esd.

Try to reproduce your problem, run limewire and then run xmms. If the audio does not work then run KDE Syetem Guard again and check to see if the the other sound system (artsd or esd ) is running. If there is a change then the sound system used for xmms has been shut down to run the other sound system.

A solution would be to change the xmms sound output setting by right clicking on the xmms main window and selecting Preferences under the Options sub-menu. The window which pops up will have a selection for an output plugin. See if there is an arts plugin and select it to see if it works.

Let me know how it goes.