Display resolution problems

a fair newbie with linux… but even newer to opensuse.
I recently reinstalled it because of some weird problem…
My problem Is now when i get to the login screen The screen does not take up the full moniter…
it is fine up top and bottom, but on the left and right side, there are a few inches on each side.
I can then login to my account, go into the display settings and change it…
it is all good.
then i shut down.
When i boot up, the login screen, and my account has the wrong resolution!

What graphics card do you have and what desktop are you using KDE 3 or 4 or gnome?