Connecting XBox to Windows 7 WMP - Detailed Checklist Required

I have an XBox 360 which I'd been using as a media extender for my desktop.
Previously the desktop was running XP Home; it now dual-boots with Windows 7
Home Premium, as does my laptop.

I find that while the XBox can connect to and browser files on my laptop,
and on the desktop while it's running XP, I can't connect to the desktop when
it's running Windows 7. The XBox doesn't see the PC at all. I can't be a
router issue since, as mentioned, it can see the desktop when it's running XP
(and also sees the laptop). I've tried a few things such as checking the
firewall, etc.

If anyone can point me to an exhaustive technical checklist of things I need
to check (including services that need to be running, ports that need to be
open, etc), I'd be very grateful.

Regards,

P.