hmm, i dont quite get all of what youre asking, so ill break it down and respond as necessary.
USB is backwards compatible. this means that a usb 2.0 devce will work on usb 1.0 input adapters. they may be slower in terms of data transferring, but you shouldn't see much of a difference on a wifi dongle. usb also as a general rule, does not require drivers, hence the "universal" part of the devices. linux is probably different, however.
most linux distros have wifi support built into them with stock basic drivers for most devices. using a USB dongle however may prove difficult. you may need to define the dongle as mounted, i'm not too sure. i know my ipod will not be detected unless it's plugged in during boot up, *but* an ipod can be seen by an OS as a removable drive, so that may have something to do with it.
linux is frustrating as hell when it comes to usb devices, i know that much. its frustrating as hell with almost anything thats removable.
i run my xbox thru my dd-wrt modded router. in both xbmc and dsl, i defined my ip address, gateway ip, and subnet mask. my router is wireless, but obviously, dd-wrt is controlling the ip and connectivity of the router, and the internet is then routed in via crossover cable.
*realistically* you *should* be able to simply plug in the usb dongle, boot the xbox, and define your tcp/ip settings. look for the control panel in dsl, and go from there. it will have your video settings, theme settings, internet settings, etc. you may also need to go to
http://197.168.1.1 in your web browser to setup the usb dongle for DHCP, static IP, etc.