How do I adjust the Windows 7 volume control over a smaller range?
I don't believe this is possible with the default Windows 7 audio controller [see this]. However third party plugins such as Volumouse or Volume2 can give smaller steps.
Volumouse is pretty basic and should fit your needs, though Volume2 supports more advanced features, such as changing the scale to logarithmic.
You could try using the up and down arrow keys instead of the mouse.