Thanks everyone for your input.

I've decided to go with premchai21's suggestion which "does math", as opposed to Monky Python suggestion which is exactly what I was looking for (I can hear everyone now... 'Is he nuts?!', 'Has he gone mad?', 'First he asks for 'no math' and then he decides to figure out the exact value of pi!', 'Burn him at the stake!').

Ah, but you see my friends, you have all taught me the error of my ways. Math did not make finding a solution more complicated. My problem was that I was not "seeing" the proper math and thus thought it would be a messy solution. In fact, because I cannot trust the intergrity of the data handed to me, math makes my inital problem easier to solve.
My fear is that $bar may be greater than the number of digits in $foo and thus I would need to add zeros in front of the number ($bar=5 $foo=1500 correct result = .01500). This could be done with reg exp, but my new thinking (IMHO) is that math would be a cleaner solution (I hope i'm not opening a can of worms here).

Thanks again everyone for the learning experience.