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In a nut-shell...
You'll first want to find out which forum script you want to use (I like SMF but phpBB is a good one to start with). Take a look at their sites as they have live demos.
Once you know which one you want to use, I suggest you get yourself some hosting (one that supports PHP and a MySQL database).
Once you have the hosting, you'll want your hosting control panel and FTP address/username and password. Log in to your hosting control panel and create a MySQL database and note the username/password.
Download the forum script and upload to your hosting, then access the forum setup address in your browser. Fill in the required info and you're pretty much done.
Best of luck :)
And seriously, count on 2 years of your posting to a blank page without anyone else helping out. I find forums take about that long before there is enough people posting for it to be self sufficient.
if you think you'll have regular members posting away in six months, you'll be disappointed in six months.
Rusty Red Widgets might not have the same allure as Bright Shiny Widgets. Even in niche markets if your forum speaks to some you'll get participation, but it will take several to six months. Get a half dozen posting (and you bouncing off each of those) you'll get the back content necessary for the search engines to spread news you exist.
It is a matter of time and perseverance.