that was probably my post on the nvidia site you saw, but my case appears to be rather unique.
To see if the nvidia drivers are working correctly is simple.
Try running TuxRacer.
Or, check your /var/log/XF86log (XFree86 logfile).
You should see a few lines (probably with (II) in front of it) that refer to your NVIDIA driers being loaded, modes, agp size, mem size, etc...
You can also run lsmod, and see if the module is loaded there
dmesg might be handy here too.
Run an OpenGL game. If it runs, you should be set.
You might want to learn to love your manuals, especially in linux. You might be surprised at the number of answers to your questions that appear in manuals.
There is no nvidia tweaker that i can think of that is a gui for linux like you had in windows. The README file (which, not technically being a manual, you might want to read) included with the drivers have a long list of options explained to them at the bottom in the appendix. I happen to be reading this now in an attempt to get my fx card to run in 4x agp.
Check it out, and let us know how you do!