Make sure you have 1.06c installed, and check up on the forum if you are behind a router, and set it up properly.
Then you go to Valkyrienet via MP options in the game, and find a group to join. To get yourself started when you're just beginning, try and post at threads of groups getting games together, as a lot of people (including myself) are weary to get unknown players in their games (because of cheaters and quiters).
When you found a group, and set a time to play (GMT time is mostly used, since their are people from many different timezones playing), get to VNET in time, and join the host.
Make sure you have some time on your hand when joining a group. It's frustrating if someone has to leave early in a session, and a session can take many hours.
With regards to game speed; most of the time the lowest speed wanted by a player is used. Time not at war tends to be on Above Normal, minor wars are on Normal, and when there is a lot of action, people tend to go to Below Normal. If you are an impatient guy, make sure to play a nation who gets to war early to keep it fun for you (ie. not US in 36 scenario). Game speed also depends on the connection. If there are many lag-issues, speed tends to go down.
Pausing is sometimes necessary for a player. I'm not aware of any rules, but in my groups, it's considered polite to refrain from unpausing if someone pressed pause. Try to pause not to often or for minor things, as you will be holding up up to 7 players their time. 1st of January tends to have a standard pause, as most players need to do things for their country (upgrading IC, assigning newly gotten ministers, etc). Pressing unpause without people being ready will probably make people angry with you

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I don't know how well your machine will perform, so no answers there.
Some general tips:
If you are new to MP gaming, I also suggest you don't play Germany, Japan, UK or SU in your first games. Playing against people is totally different then against the AI, and playing one of those will upset the game balance for the more experienced players. Playing France, a Common Wealth country or Italy with an experienced UK or Germany to give you some advice works best imho for the first couple of games in an experienced group.
Most player groups play by certain rules, often found on a HOI forum (
http://p210.ezboard.com/bdynaverse,
http://xsorbit25.com/users5/hoiplayers/index.php, this forum). Make sure you read, understand and get agreement on those rules, as it's troublesome to discuss about them in game.
Also, check the forum if you have questions about game mechanics. There is a lot of info about it spread out through these posts.
Happy gaming!