I let Melodyne detect the tempo of a standard tune.  I tamp tempoed it by hand and found it to be approximately 145 bpm.  Since I wanted to tempo map it with it's varying beats, I let Melodyne tempo map it and it came out to approximately 70 bpm.  I set a drum loop to play along with it and the drum loop plays ok but at half speed.  Same with a loop with 140 bpm.  Is there any way to maintain the tempo map of Melodyne, but yet double its value?

Not unusual at all, unfortunately. I and others have reported that Melodyne often detects tempo at half the correct value. If you've upgraded from the bundled 'Essential' version, its my understanding that you can edit the tempo map (or the detection criteria) to fix this in Melodyne. If not, your only option for proportionally scaling the tempo map to double all the values in SONAR would be this:
 
1. Select a MIDI or audio clip that runs the length of the project.
2. Go to Process > Fit to Time.
3. Convert the current Thru time to total frames (usually 30 frames/sec).
4. Divide that by 2.
5. Round and convert that new value to minutes:seconds:frames.
6. Enter that as the new Thru, and select Modify by Changing: Tempo Map.
7. Click OK. 

Extremely useful, brundlefly.  I upgraded to the Studio version at a price I could not pass up, so that might account for the problem.  I have never used the Essential version since I've always had Editor, and now Studio.  I will follow your instructions and see what happens.
 
Thanks.