Windows 7: wireless issues - drop out when sharing

Hi guys,

I've noticed quite a lot of wireless issues posted here, but after a good bit of searching, can't find anything which matches my problem.

I am able to connect to my home wifi network no problem, and my connection speeds are fine, however, as soon as my flatmate's laptop connects to the wireless network, my connection starts to play up. speed goes down, many pages hang up and require to be reloaded, and google chome displays the old favourite "resolving host" message.

• i've tried on firefox and i.e. as well, and the same issue occurs.
  
• i've tried doing a hard-reset on the router, and re-configuring settings on that.
  
• i've tried shutting down the windows security essentials and windows firewall

.

My flatmate's laptop is Win XP sp2. My laptop was Vista and we never had this issue before. it's only started since i installed win 7 (clean install) and as far as we can tell, no other variable has changed.

it's now bugging me to the point where i'm considering rolling back to vista using my recovery discs.

any suggestions?

thanks and regards
craig.

Are you running homegroup?

nope, not running a homegroup.

my computer is the only one which is win 7. there is a desktop on wired connection (which doesn't seem to have any effect whether it's on or off), and the flatmate's laptop, which is xp, and as soon as it's connected to the wireless network, my speed disappears (still shows on the taskbar as being connected full strength).

Other things i've tried, by the way, are: rolling back the wireless card driver to an earlier version, uninstalling it completely and re-installing with the latest drivers.

if i plug a wired connection in, it works fine, so it's definitely a wireless problem (though i know that covers a hugely broad spectrum).