I would to propose adding these tools, in addition to araxis and bc. Both of the tools below are free, open source and full featured compare/diff/merge tools:
For Windows: WinMerge
http://winmerge.sourceforge.net/
For Linux: Meld:
http://meld.sourceforge.net/
My favourite is meld, since it has 2-way and 3-way merge (like Araxis).
This means you can compare the old vB, your hacked vB and the new vB all in one shot, and pick and chose what to merge.