Justain's Guide to NVidia settings - Optimized for Minecraft.
My system is pretty weak. AMD x64 2.4GHz (single core), 2GB DDR2, and 6150SE (an old onboard gpu). With Beta 1.5_01 (no optimine mods, gamebooster, changing process priorities or anything like that) I get 40-60FPS on Normal, and 35-50FPS on far. I have experienced crashes and FPS drops (to under 10FPS) in the past, but I'm good now.
Check Nvdia Control panel and make sure these options are set (under "manage 3d settings"). You can adjust your global settings which will be your settings for all programs, or you can click on the "Program Settings" find your minecraft.exe and adjust it for just that game. I did both, lol.
Settings (that worked best for me):
Anisotropic filter : Application-controlled.
Antialiasing - Setting : Application-controlled.
Conformant texture clamp : Use Hardware
Multi-display/mixed-GPU acceleration : Single display performance mode.
Texture filtering : I left all of these on/allow.
Texture filtering Quality: Performance gives better FPS, but in Quality mode, everything looks smoother, so I chose Quality here.
The other settings I just used recommended Nvidia settings (indicated by the green icon in the drop menus). These didn't affect my FPS (or at least I didn't notice anything).
Also, everyone's systems behave differently, so these might not be your optimal settings, but these should be close. The most important settings are the Anisotropic filter, Antialiasing, and multi-display acceleration. Play around with other settings (safe) and check which work best for you.