Understanding Acts and Galatians
Today's passage continues in a short narrative where Paul gives an accounting of his conversion and apostleship. We have some information of these things from Acts, but the tricky part if figuring how they fit. A common break down of it looks like this:
Gal 1:16 Conversion
Gal 1:16–17 Three-year interval (Arabia, Damascus)
Gal 1:18–20 First Jerusalem visit of 15 days
Gal 1:21–2:1 Interval of 14 yrs (Syria, Cilicia: preaching to Gentiles)
Gal 2:1–10 Second Jerusalem visit for private conference on Gentile mission
Gal 2:11–14 Incident at Antioch 
Lining this up with Acts can be interesting because there isn't enough detail to know for sure. Two guesses are this:
"1. Acts 9:26–28 =Galatians 1:18
Acts 11:30; 12:25 = Galatians 2:1–10
Acts 15:1–35 (omitted in Galatians—perhaps because Galatians written before the event)
2. Acts 9:26–28 = Galatians 1:18
Acts 11:30; 12:25 (omitted in Galatians)
Acts 15:1–35 = Galatians 2:1–10" 
How you take it hinges on whether you think that the events of Galatians 2 are speaking of the Jerusalem Council in Acts 15 or not. There are arguments that could work for both sides - I actually haven't done enough reading on the issue to make a solid decision, but I lean more toward option 2 at this point. This doesn't necessarily effect the point of the passage, but is an important issue nonetheless.
So, what IS the point of the passage? Let's focus in on the showdown between Paul and Peter - what exactly is going on here? There is definitely a huge emphasis on the failure of the Law to justify us in Galatians, but I think the point of this showdown is the OUTWORKING of that belief.
Paul calls Peter out because when James comes into town, Peter stops eating with the Gentiles. I don't believe Peter would suddenly forget the content of the Gospel and think that he could earn salvation through the Law here. That's a bit of a stretch. What I think is going on is that Peter is not applying the Gospel to life. His fear of what other Jews might think of him causes him to start following the Law very closely again (not necessarily bad) at the expense of shunning Gentiles and treating them as second class (VERY bad). Hence Paul starts in on verse 15 about Jesus and the Law. He speaks of the relational truth to make sure people both UNDERSTAND it and APPLY it. He's in essence saying to Peter: "Don't say one thing and do another".
So what about us? Do we really live like we believe what the Gospel says? Or do we treat others as worse than us because they are poor or a different race or a different group of people? This passage is FULL of application for us in the US - the land of the segregated social groups. I think Paul would have a lot to say to us as well.
 Robert H. Stein, "The Relationship of Galatians 2:1-10 and Acts 15:1-35: Two Neglected Arguments", Journal of the Evangelical Theological Society Volume 17, 4 (Lynchburg, VA: The Evangelical Theological Society, 1974), 238.