It's difficult to do an exhaustive comparison in just a forum answer. However, I will mention some points as the previous answers did.
I have taken a look at it and there's not a whole lot of difference but this is what i found: 1. Runs .net instead of java.
Is a lot more integrated into microsoft (especially sharepoint)
The reporting is far more advanced.
Thats all i could find at a glance. I hope this helps.
let me put down a few bullet points that I am aware of:
the following link provides more detailed information http://www.skelta.com/products/bpm-2009/overview.aspx
However if there is someone that has used this solution it would be nice to get some hands on info.