Bicycle Mechanics - I need some schooling on Chainrings

I have a double chainring up front a 42/53. I want to replace the 42 with a 38. The current 42 is a shimano sg 42. This is being used on a 7 speed bike. When I look at chainrings I see that there are different types like type b and I think that I saw a type c. What is the difference between these types? The bcd on the chainring is 130mm and it looks like the ring is about 2mm thick and the teeth appear to be centered on the ring. Do I need to steer clear of 9 and 10 speed chainrings?

Where can I get a plain Jane chainring that will work on the bike? Is the 15 tooth jump on the front chainrings going to cause extreme shifting problems? Are there any other things that I need to take into account when I make this change?

http://sheldonbrown.com/dura-ace.html#chainrings

I ran a 38/52 on an old Shimano 600 drivetrain w/o isues, I doubt one more tooth would be that big a deal.

That was a good read but I am still confused. My chainrings don't have an A or B stamped on them so will any chainring with 130 bcd work for me?

That was a good read but I am still confused. My chainrings don't have an A or B stamped on them so will any chainring with 130 bcd work for me?

Your rings were pre-A/B days, so yes any 130bcd will work. The main point of that article was that it helps shifting to match A's w/A's. etc, but not required. The older pre A/B 6/7/8 speed rings should be cheaper than newer 9/10s, anyway.

Thanks. I guess that I sometimes make too much of basically nothing.