802.11b is only 11Mb/s, which is pretty much equivelant to 10BaseT wired networks - which is 10Mb/s. Currently, most broadband connections hover around the 1-5Mb/s area in downstream, and around 512Kb/s upstream.
In short, a 802.11b wireless network is more than enough if all you're doing is internet gaming. For now, only look for 802.11a if you're going to be doing a LOT of file sharing. Games can barely saturate a 10Mb/s connection... why would they need 100+??
Deffinitions:
Mb = Megabits (!= Megabytes) divide this number by 8 to get MB
ie.
10Mb/s = 1.25MB/s
100Mb/s = 12.5MB/s
1Gb/s = 125MB/s
and so on and so forth...