I could be wrong, but Jan. 23rd, 2006 13 seer will be the minimum, but as long as you have existing inventory of "older" seer rated units, you will still be able to use them (I realize they may not last long).
As far as the "freon" goes, you will still be able to use R-22 up until the year 2020, but...starting next year the goverment is going to "regulate" the production of R-22. I'm not sure of "R-408", but at this time R410A seems/will be the replacement freon of "the future" (AKA "Puron" and some other manufacturers "private labled" freon, but it's still 410A).
Bird, you have nothing to worry about an "attic instal" (as long as it's done properly). Very common practice in the south east where there are no basements.