Just so you all know, the Shrink Wrap addin for 2009 and the Shrink Wrap functionality in 2010 are fundamentally different, the latter being a LOT more powerful. How you ask? In addition to what has been posted above
1. 2009 addin can only produce solid shrinkwraps, 2010 can produce composite shrinkwraps consisting of only the visible faces from part solids (as compared to the entire solid in 2009) resulting in a MUCH lighter model (smaller file size).
2. 2009 addin booleans the solids together (unites them into one blob). This can get really expensive in terms of performance and is often prone to failure. In 2010 you can avoid booleans altogether by creating a multi-body solid shrinkwrap (if you need a solid result) or composite SW.
3. There are a lot of options in 2010 fpr fine-tuning the results - exclude small parts, include only parts that are more than X% visible, etc.
Just wanted to point out that the two are qualitatively different (apples and oranges...) If you can choose, go with the 2010 Shrink Wrap functionality.
HTH,
Santosh