Hi
I also found this completely annoying when I switched to the Mac from my PC. In fact it seems stupid but I nearly sent the iMac back so I know what you mean.
I managed to find a solution... I bought a Microsoft Mouse!
Once the software is installed this gives an extra button in System Preferences to tweak the mouse. Inside the Microsoft Mouse settings box you can change the Pointer Options and select IntelliPoint Pointer Speed. Setting this towards the right speeds up the mouse and takes away the acceleration problem. I have mine set about 4 bars from the right and now happy.
This only seems to take effect when you are actually logged in so the Login Screen is still the old style mouse speed.
I've been using this for about a year or so and now very happy 🙂 Its not as flash as the Mac mouse but needs must.
I purchased a basic Microsoft Wheel Mouse Optical USB mouse. This looks like the one but can't be 100% sure.
http://www.amazon.co.uk/Microsoft-Wheel-Mouse-Optical-White/dp/B000E1Z4UQ
Hope this helps.