"Private Messaging" in AmIRC

[Piru]

That can't be private messaging then. Just clicking some nick can't open window on the destination.

The only thing that I can think of is DCC Chat.

Anyway, See AmIRC Prefs, "Actions", "Special", "Other actions", "Userlist doubleclick:". You can set the doubleclick command here (it can be '/DCC CHAT %u' for example). If you don't need the other side to open up a chat window (just yourself), use '/QUERY %u'.

[Piru]

I tried DCC chat but got an automated response from the user's client saying that it was not supported

Well, it isn't AmIRC's fault the user is using some poor client...

However, use the '/query %u' thing then, but be aware that it does NOT automagically notify the target user in any way.

Only after you type some msg to the user he/she will actually see you're trying to msg him/her.