all the settings for these things are stored on the network adaptor itself, and what in sends 2 the machine is the same as a wired signal, so the xbox won't notice any difference in the signal type. but the only thing that can be effected is the amount of data being sent/howfast witch is determined by signal strength and inferance, I use Wireless-G. but u need 2 consider what ur going 2 use it for tho, if the only connections made 2 your XBOX is for XBL, then wireless-B is good enough, but if u also wish 2 FTP wirelessly, I really suggest a wireless-G network. check this out
Wireless-B runs at 11Mbps(MegaBit), witch is only 1.375MBps(MegaBytes), and 2 achive this speed u must have almost perfect connection
Wireless-G runs at 54Mbps(MegaBit), witch is 6.75MBps(MegaBytes)
Now I have wireless-G for my system, and most of my FTPing is done in XBMC, and with a Good Connection/48Mbps(Megabit), I usually can only manage 2.5MBps of data transfering
now lets put this into a time frame, say u wanna transfer a game 2 ur PC that is 2.5Gbs, with perfect speed on Wireless-B it would take you 30 minutes 2 transfer, and with Wireless-G it would take only 7 minutes, tho with all the interferance that effects wireless so easily it takes closer 2 18 mins, and since it triples the time on G, triple the B time and ur waiting a long time. tho the speed will vary from location of the Router(best 2 locate as close 2 the center of your house as Possible) and location of the Network Adaptor, plus it's best u don't put the router 2 close 2 ur Monitor, try and keep it about 2 feet away as that should help reduce some interferance.