Not too familiar with Xen or SLED but I have some tips for virtualization networking.
>Make sure everything is on the same subnet. Windows IP configuration, and any SLED/Xen network configuration (most VM products have a seperate network editor, and sometimes default the guest to a private LAN).
>Check firewall settings, can't tell you how many times the Windows firewall has blocked me from network resources when I forgot to disable or poke holes in it.
>I find best results when I "share my physical connection". This will trick Windows into thinking it's actually using a physical NIC, instead of a virtual network connection.