Well the ipronto is WORKING just fine right now due to your help.
Here how I managed to make it work. This I think applies to all ISDN subscribers (in europe it isnt so widely common and cheap DSL lines yet).
And YES the "Ad Hoc" DOES NOT work on iPronto. I turned back to the store I bought that card and got a new router+WAP.
I got a "D-Link" router+WAP in one, it has the 2 samll antennas and it is also a switch for 4 network positions. One extra port is for connecting the DSL modem on it. So I disconnected my old 5 position switcher and started using the new one which is also a WAP.
As I dont have DSL but ISDN instead I left this port unoccupied. I plugged my PC which has direct access to Internet (USB port to ISDN modem) with its LAN cable to port No1 of the D-Link.
So dont connect anything to the DSL input if you will share a computer's Internet, JUST plug this computer to the No1 port.
Next, I configured Internet Sharing "enabled" to my Internet connection(I already had enabled that feature before as I had 2 PCs, a notebook and a net printer, internet sharing threw LAN/Switch).
I runned again the "Home or Small Office Network" Wizard and I gave name of the network as my SSID.
That was it.....
All is going perfect. I connected with my iPronto to Internet, upgraded IMMEDIATELY, as per Daniel instructions and have all the pages downloaded.
The only page which denied download is the EPG, but I dont care at all, as this page is for US residents only. I will try to find the EPG for Greece TV programs.
I got some Great Help in here so I ended up with a working iPronto. I dont know where should I be without you guys.
A big thank you again to Daniel and Phil. I hope my post will help some future ISDN users.