Can't set up sharing with Airport

Question

We have a large number of Macs in the house, which previously connected to the Internet via Airport Extreme connected to a VDSL cable modem.
Lightning took out the Airport Extreme (nothing else died on the surge protected power board) so we are back to using Ethernet cabling going direct to the VDSL modem from my iMac.
I have until now shared my Internet to the other computers with a local computer to computer WiFi network using Snow Leopard.
I have now installed Lion and whilst I connect to the Internet OK, the other computer's can not connect via my Shared Internet.
In System Preferences > Sharing the instructions are backwards (not just mislabeled).
If I check Internet Sharing To computer's using: is greyed out. So I check Wi-Fi then Internet Sharing.
This let's my wife's computer finally see and connect to my shared network, but Safari and Mail never make the connection.
What have I missed?

Answer 1

Loads of stuff goes wrong with PC..
First issue is the Apple names for wireless are not actually compatible ..
So change all the names in the TC to SMB ie windows type.. that means..
Short, all names should be 2-20 characters..
No spaces and pure alphanumeric.
Set different names for 2.4ghz and 5ghz.
Then if it fails turn off security.. see if that works.. it is just a test so you need to put it back. If it fails with security on.. but works with it off.. tell us.
Regardless of the outcome..
Tell us exactly what wireless card your PC has?
Have you set the PC to be located at home.. not work not public. Turn off the firewalls.
Download the latest driver for the exact wireless card from the card manufacturer if possible.. the worst is intel cards in laptops. Some of their drivers are utterly woeful.. Apple never use Intel wireless even though they do use everything else intel.
Sometimes you need an earlier driver.. do not be surprised at all the issues.. this is where Apple never test.. why should they .. they could not care if your PC works or not.
Try another wireless if you continue to have problems.. broadcom cards are the best if you have the latest AC TC.
Finally just put your existing wireless router in wan bypass and plug it into the TC.. and then you will have perfectly fine windows connection to the network... all the non-apple colbber can connect to it.