1. Set the current time manually. Before you can use NTP, you need to have the time on your system correct to within a few minutes. If its more than an hour or so, NTP won't have confidence in the time it gets from the server and as a result, it won't update the time. As root:
date "MMDDHHmmYYYY"
where MM is the two digit month, DD is the two digit day, HH is the two digit hour on a 24-hour clock, mm is the two digit minute, and YYYY is the four digit year. For example, 6:30pm on July 30, 2009 would be:
date "073018302009"
2. As root, use YaST to setup the NTP daemon:
yast ntp-client
This YaST module is available under the "Network Services" section of the YaST2 GUI.
You'll need to set the NTP start to automatic before YaST will let add a time server. Add a public server (the tool has a pretty good list of servers you can use). Then, if you don't have a permanent Internet connection (including a laptop or a computer using the Network Manager applet), set NTP to only start manually.
3. From this point on, anytime you want to reset the time on your computer, use, as root:
ntpd -q
This will cause NTP to set the time and then quit.