Well I recently fixed JJ2 on the one computer the main one with the internet plugged into it. However the older computer which is sharing the connection wont play JJ2 :

1.It times out
2.It wont host

Ive tried disabling the firewall opening ports but it wont work. Ive looked around for help but their isnt much so could someone please help me.

What type of internet connection do you have?
What internet connection sharing software are you using?
What operating systems do you have on the two computers?
How are the two computers physically connected to each other?

This article may help, though it focuses on routers.

Operating System on both PC's is XP