The only way I was able to get my 360 to communicate and "see" files on my
laptop was to directly wire the 360 to the laptop via the supplied ethernet
cable.  I have not purchased the wireless adapter from xbox yet.  

The Nintendo Ds Wi-Fi adapter setup package turns on "Internet Connection
Sharing", which causes the UPnP service on the PC to disable itself.  To
turn off Internet Connection Sharing, go to Start->Control Panel->Network
and Internet Connections->Network Connections.  Then select each network
connection, choose File->Properties, select the Advanced tag and uncheck
"Allow other network users to connect through this computer's Internet
connection".  Simple, eh?  Note that this will likely disable functionality
of the Nintendo Ds Wi-Fi adapter - to re-enable it, re-check any of the
"Allow other network users to connect..." boxes that were unchecked.

See http://forums.xbox.com/1496963/ShowPost.aspx for some more details.

Okay, I've found a fix that works for me.

Make sure you are on an administrator account.

Press Start
Right Click on "My Computer"
Choose "Manage" from the context menu.
When the Computer Management console appears click on the Services and Appli
cations icon in the left hand pane, and then the Services icon that appears
as a child directory.

In the right hand pane do the following for both the "Universal Plug and
Play Device Ho
st service and the SSDP Discovery Service:

Double Click on the service.
Ensure that Startup Type is set to "Automatic"
Choose the "Log On" tab in the services properties dialog
Choose the "This Account" radio button in the "Log on as:" section.
Type "NT AUTHORITY\LocalService" without quotes in the text box.
Don't change anything in either of the password fields. If it requests that
you change the password, clear the field.

Hope this helps!