You can get some of them by going into
YAST -> System -> Runlevel Editor
and disabling the ones you don't want running. Just know what each service that being started in there is supposed to be doing for you before turning it off.
The other place to look would be in the files under /etc/xinetd.d. These are where the "on demand" services are set up. If you're seeing constant slowness, I rather doubt that these services are you problem. If you don't need some or any of these turned on, you can disabled them by editing the file and locating the the line that says "disabled = no" and change that to read "disabled = yes". Then inform the xinetd process to reread its configuration. (See the "xinetd" and the "kill" manpages for details on how to do that.) Another reason I doubt this is your problem is that the xinetd service isn't started by default on SuSE. (It's not in 9.0 and 9.2, anyway.)
Try running "top" to see if there are any CPU hogs running. There's also "ntop" which is supposed to be like "top" but displays what processes are using the network and how heavily. I cannot tell you much more about that tool, though. (I've only tried it a bit and haven't gotten much experience with it yet.)
Another thing to watch out for is tabbed browsing. I've seen cases where I'll have had a bunch of tabs opened and several of them were running some silly animated graphic over and over and over... Also, you haven't done anything like enable debugging on some service have you? The logging of the debug messages could be a problem. It's not uncommon for folks to forget to turn it off once they've solved a problem that required enabling it. (Your log files get pretty huge as well.)
Hope some of this helps...