Hi Andi,I to am now an overpronator having been told I was a neutral.
I have had loads of calf problems in right leg to the point i saw a podratrist two weeks ago his findings were eye opening.
In stance all was fine various muscle lengths were fine,gait was "as good as it can be barefoot" my problems arose when i put my nike air pegasus 28s on both ankles collapsed more so on the right to eye watering proportions.I also had a pair of adidas tempo 4s that i have worn which gave a better finding the difference being the torsion control in the adidas making them more rigid in the midsole,he told me to run in these to see how i fared, not good calf pull third time out.Have been looking now at minimal shoes to get closer to natural gait but long way to go.Have a look at runblogger .com some in depth articles on there you may find helpful.
I agree with seren nos the first half to a mile i feel is the hardest part but it does get easier,make sure if you can your route is flat, uphill at the start can put you off. you might find going out in the evening suits you better.Try running at the start and stop when you have to and walk try to time yourself and go better the next time.You will soon be doing a full mile and more.....