The OP has downloaded OpenSUSE with Gnome, that means live gnome cd
You will need a broadband connection to install these.
So to install KDE:
1. Press Alt and F2
2. Type
yast2
and press ENTER
3. Key in your password and press ENTER
4. Click on Software->Software Repositories, and enable the three repositories you see there, namely, OSS, non-OSS and updates. If they are already enabled skip this step.
5. Click on Software Management. When you open Software Management for the first time it will refresh the repositories. Wait for this to finish.
*img401.imageshack.us/img401/2194/gnome1qv3.th.png
6. Click on Groups and change to Patterns as shown
*img406.imageshack.us/img406/3551/gnome2ez6.th.png
7. Scroll and look for KDE 3 base system, select it, and click install
*img207.imageshack.us/img207/8590/gnome3ph1.th.png *img207.imageshack.us/img207/1161/gnome4dq2.th.png *img207.imageshack.us/img207/5430/gnome5ux1.th.png
8. Do the same for KDE 3 Desktop
*img407.imageshack.us/img407/7224/gnome6zl1.th.png
and click Apply
Now reboot your system, and at the login screen use the mouse to select your session type, and then login.
In case you auto-login after rebooting the system, then just logout and then change your session type, and then login again