Im trying to create an S-function which will read/capture
data from hardware in a system, which will then be used in a
Simulink model.

The hardware drivers and hardware API makes use of ".dll"
files. Is it possible to include/use these .dll files in a
Simulink s-function so that the functions within can be used
in the C MEX S-function?? 

If so will you be able to give an example or directions? All
attempts so far has led to syntax errors or the following:

error LNK2019: unresolved external symbol __imp__fntest_dll
referenced in function _doubleIt 
test.mexw32 : fatal error LNK1120: 1 unresolved externals 

Thank U
Jeffrey