To summarise:

We tried some time ago getting David's XP notebook and his Win7 desktop to share the Internet connection that his desktop has via an ADSL modem and telephone line.

We wanted to get the two PCs to communicate with each other via the Wi-Fi adaptor card in the desktop and the built-in Wi-Fi adaptor in the notebook and then to share the Internet connection. We had no success.

Last weekend we tried to get David's Win7 laptop and Win7 desktop to share the Internet connection that his desktop has. No success again.

At the moment each computer lists the other one in its "My Computer" page.

The TrendNet Wi-Fi software in the desktop indicates that it has 100% signal strength from the laptop.

Both computers are set to "Home" type networks.

We can start a Home Group on either computer but cannot get the other one to join - an error is reported. We use the correct password when trying to join - the password displayed by the other computer when its Home Group is created.

We cannot get the ICS service to stay started. After attempting to start it an error is reported that says "ICS service started and then stopped".

We have checked all ICS's dependant services and they are all running.

Ad Hoc Internet Connection Sharing @ windows7forums

Don't know if it will help, but worth a look. Be sure to read the entire thread (3 pages).

Resolved - Trendnet 300 Mbps Wireless N PCI Adapter TEW-623Pi is not compatible with Win7.

Win7 inhibits the IP Configuration Address from being shown.