I've become convinced that I could more easily learn to write a DLL, even if I only have extremely limited experience with C++, than to write an mIRC script to do this.
Thanks for your help, and I think I have a better understanding of how this sort of thing works. If I fail at the DLL, I'll just work more on the script..
If you were wondering why I needed this, I was writing a simple encryption algorithm using mIRC scripting. When I think about it, it really isn't all that great.. so I'm not sure if it's worth the effort.