It seems alot of people are having random disconnect issues using wireless , i have a few ideas that although are not definate fixes have worked for me and a few friends , these fixes i have come across myself by trial and error and a little knowlage ;)
First thing assign a fixed IP address to your XBOX via your router , there are alot of differant routers out there so i have to be a bit vague . Your looking for a list of connected devices in your router so your looking for a heading with something like "home network" or "connected devices" as a title. Next you need to find your XBox in that list it will most likely be listed as a mac address looking something like "unknown 64-68-0c etc" . Next select the device usually by a double click and your looking for a heading looking something like "Always use this ip address" or "use fixed ip address"
Next manually set yourt wireless channel most likely found in the wireless section (no sh!t sherlock) if wireless channel is set to "automatic" change it to channel 11 then apply and save etc
one more thing the xbox doesnt seem to like is wireless N , disabling this can sometimes help , yor looking for something like "wireless interface type" its most likely set to automatic or 802.11 b/g/n , it wants to be set to 802.11 b/g effectively disabling N , this will decrease your wireless range (you most likely wont notice) and it will decrease you file transfer speed between pc's (once again you you'll probably never notice) but it may help your disconnects