Well,
I phoned zen internet, and they said that the speedtouch was fine, and all you have to do to it is....... and then talked at me for about 15 mins on what to do (I love techies... "all you have to do is...")
I did it, (port forwarding) but it still didn't work. I told him I thought it would work fine putting it into bridge mode, but I couldn't do this.
Zen also told me that I was the first person to ring them regarding iChat not working. Well, I must be very unlucky.....
So I got in touch with speedtouch support (which is almost non existent, email only, no downloads) who told me the same. I told them I tried port forwarding already, didn't work, so they told me to assign the public IP to the time capsule.
That didn't work either (My time capsule for some reason disappeared - some kind of IP clash or something??)
So, I managed to find a firmware update to my router (speedtouch support wouldn't give me it) on some random German site, and after 6 (SIX!) attempts, it installed (I had to boot my Mac into PC mode...). I've never seen something install bit by bit, bombing out every time, but a little bit further on the way...
This update gave me an option to configure my speedtouch in 'Bridge mode'. I then configured my Time Capsule to connect to the internet via PPPoE, and....
It all works!!! woohoo!!!
Unfortunately, the other two speedtouch routers don't have the bridge option despite having exactly the same firmware version.
I figured that instead of messing about anymore, I should go out and find an ADSL bridge modem.
Not very popular, I suppose obviously, but I eventually found a TP-LINK TD-8840 ADSL router that went into bridge mode for £20.
replaced my speedtouch and ....
Works wonderfully.
So, if anyone wants to use iChat for video conferencing and screen sharing, I can definitely say, get zen, TP-LINK TD-8840 and put it into bridge mode, and stick this into your Time Capsule / Airport Extreme and set it up in PPPoE mode.
I can now offer this to our clients, which will save on travel and allow me to spend more time with my family.
I hope someone finds this useful.
I only posted this for therapy.
Gwyn