Q:  How can I detect the presense of a DLL that may or may not be loaded?

A:  If you mean "presence in memory", then use GetModuleHandle with the DLLs module name.  If it returns 0, the module is not loaded. When you get a valid handle better check the filename with GetModuleFilename since you may have a freak match with an EXE module name (its rampand chaos out there as far as module names are considered).

If you mean "presence on system", just try to LoadLibrary the DLL.