What does it do? Will it fix the issue that I am having with my mIRC?
Possibly. So far, what you have mentioned matches exactly all the other cases in which this fix worked (down to the fact that you're using an AMD processor). There is a README text file in the zipfile I linked, which explains things a bit better. You could just give it a try, it's harmless otherwise.
Some of the older related threads: here
. If you search for "iphlpapi" in the last 4 years in this forum, you'll find these and others.