Try this one Steve:
http://www.letstorquebhp.com/calculator.asp
I have found it pretty good, tis based on historical data. My car is 170 bhp and 540kg, program says 0 to 60 in 3.9s and my car did it in 4.1s with crappy road tyres on. Will be putting Toyos on soon and will certainly get down to 3.9s or better.....
Standard tyres seriously let the time down as having to control all power of the engine balanced through the clutch and throttle to get optimum traction. Happy with the sierra standard dif though, once you put loads of power through it you get equal drive to both wheels leaving parallel black lines all the way down the road (private of course).
AndyH