802.11a has a range that is 7x less than 802.11b. (Computer Networks, A. Tanenbaum, p. 295).

If you're interested in short range, fast, wireless communications, look into bluetooth, the chips sell for <$5.

I've got a feeling, however, that you don't want to do that. 802.11a and b are not compatible, although some cards may be 'a' and 'b' compatible. The Cisco Aieronet card I believe is compatible with both since my friend and I always sit next to the wireless router at the university and get >11mbps rather than 11 (max spd. 'b').