Googling "
hunspell richedit" (or aspell) shows that it's very much a nontrivial integration. That search returns very few resources and many people asking how to integrate the two with very little success. It might be possible, but it's not trivial. Definitely not 5-7 minutes. Otherwise you (or somebody) would have done it by now, instead of posting about the need to implement spell checking.
Frankly, if it really is that trivial to make, and is meant to be opt-in for the few who need it, this seems like DLL territory to me. As a DLL you'd be able to keep it up to date way quicker than mIRC could, which might be useful.
