What Linux Distribution with version are you using? Also, list the kernel version number if possible. You can do this by typing on the command prompt:
One reason that you can only root xmms as root is probably the file permission to you binary file for xmms is not set properly. Also, include what version of xmms you have. opps, probably missed it in the original post. This is the command I used with also shows the currently working directory of where the xmms binary is located.
$ ls -l xmms*
-rwxr-xr-x 1 root root 1079145 Sep 2 2002 xmms
To read and change about file permissions, type the following.
In my case, the file permission setting is set to the following:
$chmod 755 xmms
This way, any user, not just root, can execute the file.