This is a good intro to installing and using VirtualBox on OpenSUSE 10.3
Basically, the virtualbox which comes bundled with opensuse is the OSS version which doesn't work very well on various fronts. So unintall it..
Then download the prebuilt binary for OpenSUSE 10.3 available at http://www.virtualbox.org/ and install it.
Next, add whichever usernames you want to give access to virtual box to the group vboxusers (easiest done through yast2)
Now run the command "virtualbox" and enjoy !