StateAardvark

If so, how do accomplish that? Can you use C to do it?

can-you-create-your-own-externals

Look at the dev forum, there are also tutorials :

http://www.music.mcgill.ca/~ich/classes/mumt402/MaxMSPExternalsTutorial3.0.pdf

http://gurnig.com/asset/pdf/IntroductionToWritingExternsInC.pdf

and if you want, there are a lot of open source projects :

Look at the dev forum, there are also tutorials :
http://www.music.mcgill.ca/~ich/classes/mumt402/MaxMSPExternalsTutorial3.0.pdf
http://gurnig.com/asset/pdf/IntroductionToWritingExternsInC.pdf
...
and if you want, there are a lot of open source projects :
Jamoma
my library
....

Can you create your own externals?