Wireless ad hoc netwoks

I have a Linksys 2.4Ghz wireless network setup in my basement. I have 2 PC’s upstairs and one of the PC’s is able to get the full signal strength and works fine with the connection from the access point. This PC runs windows 2000. However, my second PC which is a windows XP which is in another room nearby is only able to run at 2 or 1 % of the signal strength at most times. Even after getting connected the signal breaks several times and causes inconvenience.

Can I set up and adhoc wireless network where the XP PC will talk to the 2000 PC rather than the access point, since the 2000 PC is in the next room? If so how would I do it? Also what should I do to enable the internet access since I wont get an IP address from the Windows 2000 machine?

Thanks in advance !