It isn't.. it never USED TO BE anyway. Now it is difficult because for the past couple years both company's (ATI, NV) drivers are total crap in many ways- including changing image quality settings. NV drivers are the worst.. buggy and unstable at best, totally nonfunctional at worst.
NHancer helps, bet sometimes that doesn't even completely do the trick because the guy writing the program has to keep catching up with the idiotic driver changes/malfunctions/bug/etc....
I gave up on ATI a long time ago- stupid drivers that take up all your ram and are slower, then NV went the same way with the "new" control panel that actually just takes many functions away compared to the old CP and "coolbits" and other tweaks. --EDIT-- and breaks profiles.
It is not your fault, it is just crappy drivers.
[/end rant]