I will assume that the nvidia driver is correctly installed from your post (basically the installer produced no errors).
To start, don't use SAX2/YAST for the graphics card config. Instead, first use sax and get all your input devices sorted out as well as your monitors.
Next, open you XF86Config file and go to the section "Device" And enter as follows (similar to mine, but change as required):
BoardName "GeForceFX 5200"
Option "NvAGP" "1"
Option "TwinView" "1"
Option "ConnectedMonitor" "CRT, CRT"
Option "TwinViewOrietation" "RightOf"
Option "SecondMonitorHorizSync" "30.0-96.0"
Option "SecondMonitorVertRefresh" "48.0-160.0"
Option "MetaModes" "1600x1200,1600x1200; 1600x1200, NULL; 800x600, NULL
O.K. all the options should each be on one line if anything appears wrapped and Case matters!
To get both monitors:
Option "Twinview" "1"
To get 3D accel:
make sure there is no option saying "no accel"
To set screen orientations to each other use the TwinViewOrientation option and make sure the ConnectedMonitor option matches your device (you can mix).
To set resolutions:
use MetaModes option and set the resolutions in pairs as above. If an app only uses one screen (like tuxracer) then null the second. The application pics resolutions from left to right, so when I run tuxracer it picks the 800x600 because it only wants one screen.
The resolutions in the Metamodes will look at the defined modelines in you monitors section so make sure those are correct. To set custom mode lines use xmode. example of xmode:
%>xmode -r 100 -x 1600 -y 1200
Modeline "1600x1200" 249.60 1600 1616 1968 2280 1200 1200 1218 1253
-r option is refresh rate and -x and -y should be obvious.
If this doesn't help then maybe you can email me your XF86Config file and I can make some changes and fire it back to you.
The nvidia help file also contains all this in the appendixes if you want further details.