paddymac,
to CF.
First off, I would recommend not bumping a 3yo thread - better to start your own.
Yes, in theory you can share an internet connection - XP refers to it as 'internet connection sharing', but it's not great. For starters, the PC will only have access when the laptop is running and plugged into the ethernet cable. Assuming it's a windows laptop, searching for "internet connection sharing" on microsoft.com should give you a walkthrough.
If your wireless signal reaches down there, why not get a cheap USB wireless adapter to dedicate to this PC.