[Asterisk-video] help for videocall

[barbara_b02 at libero.it]

Hi list,
first of all: sorry for my bad english...
I'm new to Asterisk world... I'm using Asterisk-1.4.13 on Debian distribution.
I've tested with success loopback, mp4play, mp4save and IVR calling Asterisk with a 3G mobile phone.
Now I'm trying a 3G<->sip videocall (using a NEC-phone and X-lite running on Windows) but I think I'm confused about how to do this... I've read the mailing list archive, the pages on VoIP-info and the instructions on Fontventa but I don't understand how to write my dialplan, especially the order of the following exten...

- h324m_gw()
- h324m_gw_answer()     
- h324m_call()
- Dial()     

I found contradictory configuration examples reading the archive...

And do I need the following exten?

exten => dial,1,Set(CHANNEL(transfercapability)=VIDEO)
exten => dial,n,NoOp(transfer=${CHANNEL(transfercapability)})
exten => dial,n,Set(CHANNEL(userinformationlayer1)=38)
exten => dial,n,NoOp(ul1=${CHANNEL(userinformationlayer1)})

...or maybe I mistakes configuring my X-lite...

Thanks very much for any help!
Barbara B.