You are going to want to read the entire section on DLL files over at
http://msdn.microsoft.com.... there are actually a lot of things you need to know about DLLs, such as thread safety (same process and multiple process threads)... as well as what operating system you will target your DLL files for, and how some operating system and older DLLs operate (there are considerable difference between the memory mapping of a DLL file for Windows 95 and Windows XP).