I think there's something that you (M_A_) are overlooking: Hash tables, by definition, are fundamentally unsuitable for what I understand you to be looking for. This is because the mapping of a value to be hashed to the resultant hash is explicitly and specifically not guaranteed to be unique or reversible. That means that even if you have functionality to look up via the unhashed value, you're not guaranteed to get the answer you're looking for - depending on the hashing function used, hashing alphabetic.host.name.from.here might well generate the same hash value as host.name.from.there.with.bogus.ip - a phenomenon called 'hash collision', and one that is well-known. In a case of collision, how is mIRC - or any program doing hashing - to know whether this is the same value as was hashed before, or merely one that collides? The answer, inherently, is that it can't. The functionality you appear to want seems to be best served by a database where you can guarantee non-collision. How that database is implemented is not specified, and may not matter - except that hash tables ain't the answer. If mIRC were infinitely scriptable in any extant computer language, I'd tell you to look at the TABLE facility in SNOBOL, which appears to be ideal for your needs - but not within mIRC, and I'm not aware of any SNOBOL scripting engine that could be "hooked" into mIRC.
My recommendation is to go back and examine your needs, study and understand the tools that are at your disposal, and then see how best to use those tools to meet your needs. Without focusing on one particular tool that looks cool or is fast or whatever it was that made you decide that hashtables would be the answer "if only".