tach frequency to voltage

I see two problems with it the way you drew it -

First, the Atmel microcontroller is a 5 volt device, if you run a 0-12 vdc voltage to it it won't like that - you will either need to power the frequency - voltage chip with 5vdc or you'll need to scale the output of the chip to 0-5\vdc.  Powering the chip with 5vdc is obviously the easier choice.

The second issue is the scaling of the chip in the config you posted.  The diagram states 67hz per volt (at 15vdc).  You're range will barely hit 67hz so a 1,000hz frequency range is WAY too wide for your application.  You would want to something closer to a 0-100hz range which is actually convenient because most likely you can just adjust one component by a value of +/- 10.

Now, keep in mind I've never actually got one of those chips to work right, so I may be completely wrong about both concerns (although I do know the Atmel chip won't like anything above 5vdc). 

You will have to adjust something, I'm honestly not sure what.  I know the calculations are given in the datasheet, you'll have to go by that.  I would think 20hz/v would be an acceptable range, but I'm not sure exactly what you are trying to do.  To get the most accurate output from the chip you really need to know what the frequency will be at redline and then you can scale the output accordingly to represent your range from not running (0hz) to redline (xhz).