Starcraft II – How to play 1v1 on local LAN

According to a post by a Blizzard employee, you might be able to play with your friends no matter where they are:

Getting people online, playing and interacting is obviously the overall goal for the Battle.net platform, and that includes allowing people to play across regional boundaries as they have in the past.

Unfortunately, there are a multitude of challenges we have to overcome due to the unique regional account and billing options that didn't exist in the past. But those hurdles aren't insurmountable, and we are looking into solutions that will allow interested players to obtain access to other regional versions without having to buy another full copy of the game. Those solutions are something we're currently planning to have available through Battle.net Account Management within the first few months of StarCraft II's release.

Before that solution is implemented though, you're correct in that you'd need to purchase a US copy of the game on launch day to play in the US region.

However notice that he is talking about a potential future feature which may end up not getting implemented (or not implemented in a satisfying way), so in the meanwhile I would be careful about which version to buy.

You can play with low-level computers on your team vs. your friends. I am not a big fan of uneven teams insofar as having a different number of players on the teams. A good compromise is giving your team an easy or medium computer, depending on your friends' skill levels, to help compensate. You cannot coordinate with your ally while they can coordinate with each other.

If you want to play with only one friend, you can alter this idea by giving him a hard or insane ally while you still have your easy or medium ally. Experiment with the difficulties until you find something manageable and challenging for both sides.