The final few days of the daily download series will be dealing with the use of VBA, starting with linking to C (and C++).  This was covered in:

Linking Excel to C
Linking Excel to C – 2
Linking Excel to C – 3; Avoiding bottlenecks

The download files are:

http://interactiveds.com.au/software/WalkThrough2.zip
http://interactiveds.com.au/software/Cubicdll.zip

Benchmark of cubic solution routines