Maybe I'm being a fraction short of two planks here, but I have NO IDEA about hosting my own website... this is eventually gonna be a heavy use site..
That's, how shall I say, amibtious

however, if you take it one step at a time, it's perfectly achievable (well, as long as you don't use Windows -- it may
seem to be easier initially (obviousl familarity) but if this is ultimately to be a "big" site, you have to stop thinking of the box as a "PC" and start thinking of it as a "server" (e.g. cars and lorries are superficailly similar, but...)
I'm creating the website at the moment, have the domain name, will have the server and ASDL connection set up soon...
From your ADSL line remark, I'm assuming that you will, at least initially, be hosting it "at home".
how do I HOST it tho? Do I need Win2K Server?
Only if you cannot be persuaded to use Unix (of which there are a number of flavours -- see below). Unix is "the" way to go here... big sites (as you aspire to) require seriously experienced Windows admin skills to keep the site running smoothly.
with the facilities of PPRUNE (forum, chat, member database, profiles for them and probably internal messaging as well... not related to aviation tho).
Very briefly, you'll need to go through the following steps (whatever operating system you are using):-
1. Install the OS, then
patch it and
secure it. You will
have to do this whether you use Unix or Windows.
Of the Unix-like OSes that are around today, personally, I prefer
NetBSD for use on servers, but you may find
FreeBSD slightly easier to install (but slightly harder to secure.) I'm not personally a great Linux fan (for reasons I won't bother to go into here), but these days it's perfectly adequate and still much better than Windows

. Both of these can be downloaded for free from the net, and over an ADSL link shouldn't take too long. If you want to play before your link is up or if you cannot burn a CD, PM me and I can send you a CD.
Patching means installing the vendor supplied security patches (pretty much daily, if you are using MS

).
Securing means removing
all the software and services that you don't need. Every service that you leave running that you
do not need is a potential way into you system for an intruder.
2. Install your webserver (probably
Apache, but possibly others) and your "website."
3. Install your Bulleting Board software.
YaBB is a good place to start, as it's free and doesn't need a SQL database backend (but because of that, it won't scale to the size of PPRuNE

)
4. You'll probably need to setup/configure an email system as well.
Exim is a great place to start.
Phew, there's quite a lot to get to grips with there, but take it one step at a time and you'll get there. But like learning to fly, there are no shortcuts if you want a secure system (cf. you want a safe flight.)
If you are actually hosting at an ISP you will only have to do
some of this... the more the ISP does for you, the less flexibiltiy you will have yourself; and, conversely, the more flexibility you have yourself, the more responsibility you have to take for your own actions...
Most of the above could do with need exapantion/further explanation, but I don't I have time right now, but I'm happy to continue this either here, or in PMs if you prefer to keep it private. I'm sure others will chip in to expand further, disagree with my suggestions

, etc.
HTH