Internet Connection Sharing: Can't stay connected to Network

Hi, a little help please, if anybody has a moment.

I have a wireless broadband modem, attached via USB to my iMac. I share my internet connection with a MacBook and an iPhone, across a wireless network provided by an airport express adaptor.

When I choose in system preferences to 'share my internet connection', the iMac straight away establishes its own wireless network and the airport icon in the menu bar is replaced with an 'internet sharing' icon. I then have to go into network settings and reconnect to my airport express's wireless network.

Fine to do this once. But I have to do it, pretty much every time I wake the computer up from sleep.

I don't wish to use a wireless network provided by my iMac, as security is minimal and my printer is connected to the airport express adaptor.

Does anybody know of a way to stop this happening?

I don't think I'm following you completely. Why are you connecting your iMac to the wireless modem with USB? Why not use a ethernet cable? Also, if your MacBook and iPhone are using the wireless to connect, why are you trying to share your internet connection from the iMac? Aren't the other two connecting to the modem/router directly?

By wireless broadband modem, I mean the variety of wireless broadband provided by mobile phone operators. i.e: USB modem, SIM card and dreadfully slow connection! Cant plug the modem straight into Airport express so must share the connection across a wireless network.

Does that explain things a little better?

Yes, now I see what you are doing more clearly. I'm guessing you've already looked at docs like this: http://docs.info.apple.com/article.html?path=Mac/10.5/en/8156.html ?

Thyamine said:

Yes, now I see what you are doing more clearly. I'm guessing you've already looked at docs like this: http://docs.info.apple.com/article.html?path=Mac/10.5/en/8156.html ?

Click to expand...

I created a computer to computer network using the instructions on the above link and my other computer finds and connects to this one but won't let me browse the internet. Is there something more that I need to do?

I have exactly the same problem as olaf-the-hairy.
For my knowledge the proposed link shows how to set up the canonical 'internet sharing' (the one that olaf-the-hairy already tested ), so, this could no be the solution.
I've heard that it possible to use the natd daemon at such purpose ..... if someone could help on this ....!?