The normal warnings need to be put here. Anytime you download and install a script that you, yourself, didn't write, you are inviting problems into your computer. While plenty might be worm/virus/backdoor free, there are many others which are not. Not many web sites have the resources to check every script they list. Anyone truly interested in mIRC will encourage you to write your own script. Start small, adding the items you yourself want and need without the bloat/fluff that many scripts carry.
Should you decline to write your own, consider yourself forewarned