the /opt directory is something like Program Files in windows. however, i think (if i remember correctly), it's not necessarily there for all distributions.
what's supposed to be in there? well, anything that goes into your program files in windows, i guess. i think kde and gnome is supposed to be in there (though at this point, i'm not very sure). there are also some alternatives to /opt, such as /usr (for the more common/basic linux commands) and /usr/local for the other packages. this may also vary depending on which unix/bsd/linux you use.
the sound server fatal error just means that either the device is not there, has not been detected or is not configured properly.
everything works okay as root because root has permissions to everything. i have a strong suspicion that you can't use kde properly as a user because the permissions for the kde stuff have not been extended to your user account. try looking for the kde directory or the kde command ("find kde" or something... sorry can't help you here coz i don't have kde on my box). then change it's permissions to r-x--x--x. if you don't know how to change permissions, type "man chmod" to see the instructions. if that doesn't help, then post up and let's see what we can do...