I found some great code called SimMetrics that mathematically calculates the similarity of two strings, returning a value of 0.0 (not a match) to 1.0 (exact match).
It is written in .Net 2.0, so I wrote a COM wrapper and installation package so I could use the feature in Excel. It could also be used in AutoIt.
The installation package (which installs the SimMetrics dll, wrapper dll and example au3 code) can be downloaded from here: SimMetrics COM Wrapper
Some examples of use could be: