In Windows XP, you can have whole-pixel anti-aliasing by setting "Use the following method to smooth edges of screen fonts" to "Standard", or have sub-pixel anti-aliasing (for LCD monitors) by setting the option to "ClearType".
In Windows 7, I can no longer find a way to enable whole-pixel anti-aliasing, which gives the best readability on DLP projectors and CRT monitors (these screens do not follow the RGB or BGR pattern found in LCD screens). It is either ClearType or no anti-aliasing at all. I tried a 3rd party tool (ClearType Switch) but unchecking "Use ClearType" while leaving "Enable smooth edges for screen fonts" checked disables all forms of anti-aliasing.
How to turn off ClearType and use whole-pixel anti-aliasing in Windows 7?
Edit: According to Microsoft's blog article "Engineering Changes to ClearType in Windows 7", enabling "Smooth edges of screen fonts" in Performance Options and disabling ClearType with ClearType Tuner would give you grayscale font smoothing (i.e. what I want). However, this is simply not true. It disables all forms of anti-aliasing (or, in their terminology, it gives you bi-level rendering).
And to clarify, I'm talking about changing the system default setting, i.e. the one that would be used if the application do not specify its own.