I'd vote for IRC too. Not every people love the messenger applications you're referring to, but typically a lot of people who know the things you'd like to ask do sit on some IRC channels - usually more than one. On IRC you can leave messages and have them answered (that depends on the will of the receiver of course) at a later time, if you just leave your client open. You can (and many do) run an irc client on a remote server, maybe on screen
, and have it run there even when you have logged out. This way you can collect any messages or conversations even when you're not there - just look back when you are back on line, and see what was talked about. I'd say IRC is far better than any of the candy-looking (not that IRC clients couldn't look good - most of them just stick to the functionality instead of outlooks) MSN/ICQ/Jabber/other messaging clients.
Anyway, it's up to you what to use, but I've noticed that on IRC it's more probable to get help (and faster) than on the other IM things. On the other IM apps you typically talk to one person at a time (and certainly do not have a conversation with 300+ persons times seven channels), and if that person isn't there...well, then you don't get answers. On IRC there probably is somebody who can help, maybe more than one, maybe two hundred. Another matter how willing they are to help, but in places like #ubuntu they ought to be
Note that the channels can be on different servers - many Linux-related channels are on Freenode (irc.freenode.org), but there are other servers as well. If you can't find your help at one place, just launch another server and/or open some other channels, and try again. Freenode doesn't allow you to have private conversations (if I'm right) at least before you do some sort of registration (d'oh, they're making it difficult..), but that's one of the rare networks that force you do so - and if you take the time to register, you can have (instead of your own channels) private conversations, if you want so.
Typically Linux distributions have an IRC channel named after the distribution - #ubuntu, #slackware, #fedora, ... so try those out for a start. And the IRC client..well, if you like it grahpical, maybe XChat (xchat.org) is a nice start, but if you're ok with console (which you ought to be if you want to run this remotely, which enables you to have the client up 24/7), then try Irssi out (irssi.org) - takes a moment to learn to use it, but when you do, you probably don't want to switch anymore
Or then you do. Up to you.