What you are experiencing is the pointer acceleration built in to Mac OS X and its mouse driver. By "floatiness" I presume you mean that, at slow mouse speeds, the pointer moves slower than the mouse itself, and vice versa at high mouse speeds.
I recommend that you download and install the MouseCommand mouse driver from www.macmice.ca at:
http://www.macmice.ca/itoolkit.asp?pg=Support
This will give you a bit more control over your mouse behavior via your System Preferences. You can set the Custom Pointer Acceleration to Zero (all the way to the left on the slider).
You may need to play around with the tracking speeds between the MouseCommand preference pane and the normal Mouse and Keyboard preference pane. For your reference, my normal Mouse and Keyboard settings have the tracking speed all the way to the left (Slow), and my MouseCommand settings have the tracking speed all the way to the right (Fast). This setting gives the most ideal mouse movement, in my opinion.
Alternately, you can try USB Overdrive, which adds similar functionality to the mouse driver, but I have had better luck with MouseCommand.
Hope this helps, and good luck!
John
