I had a similar problem with my house. This is a big old Victorian property with loads of solid walls.
I could not get reliable wireless coverage throughout the property. The solution that worked for me was to add a 'wireless access point' as a signal repeater.
The main wireless router gives me coverage at the front of the house and is bridged across to the WAP at the rear of the house. The combination of the 2 points now seems to work just fine.
Looks like Belkin do a unit matched to your router.
http://catalog.belkin.com/IWCatProdu...duct_Id=278082