On OpenSuSE 10.3 you can do all these configurations using Yast. In case you've never used it, go to KDE Menu --> Applications --> System --> Administrator Settings (YaST). Enter the root's password, then click on Network Devices --> Network Card. In the list of devices, select your Ethernet card and click Configure. Fill all the relevant fields and click on Next/Finish.
Regarding the proxy, in Yast click on Network Services --> Proxy, then check the Enable Proxy box and fill the relevant fields. You also have to set the proxy in your browser. For example in Firefox go to Edit --> Preferences --> Advanced --> Network --> Connection Settings.
Depending on the way you connect, you may have to configure your modem or your DSL device. You can find the proper tools always in Yast under Network Devices.