Mikey,
As Labviewguru said, calling a LabVIEW DLL is no different than calling any other DLL from C. You will need your LabVIEW DLL, the .lib and .h files for your C code and the LabVIEW Run-Time Engine for the version of LabVIEW that the DLL was built with. Other than that, everything else is the same.
Randy Hoskin
Applications Engineer
National Instruments
http://www.ni.com/ask