Wireless "A"?

Well since neither of these laptops have PC card slots, and Apple doesn't make 802.11a cards, the only way to get 802.11a is presumably thru an external USB wireless adapter, but I don't know if any support Mac.

Yeah, you are bummed. Why a school would want to do that is beyond me. You will need a PC Cardbus slot to get a 3rd party wireless card that supports the "a" standard. There's gonna be a whole lot of pissed off students with b and g cards in their laptops.

What kind of school? (high school / college)

What is in the computer labs at school? If they are PC labs and not Mac labs... then you understand the marketing that is Centrino now.

Intel is releasing a Centrino based 802.11a/b/g chip by the end of the year. Such cards are already available from 3rd parrty vendors, but are not "Centrino Certified." Apple has made no anouncements regarding tri-band cards.

802.11a is the best choice when dealing with a large cluster (50+) of wireless stations to cover a large area, such as a school. The speeds are the same as 802.11g. The difference is the operating frequency, 5GHz for a, while b/g use 2.4GHz. 2.4GHz is a very busy spectrum these days, between 802.11b/g and cordless phones, as well as being succeptible to microwave interference (both oven and other sources). For a large network to span a large area in a way that is invisible to the user, 802.11a is the best choice right now.