Hi James,
yes, it's true. At the end I found the solution through Apache (on the second server), rewriting each url appearing on all php page links. I would have liked to changes just an option in the config file (maybe one of the 'base_url{}') as easier way, because I did not experienced this issue in other php websites, buy I don't think this lead me to something useful.
Anyway now it works, even if this is not the best way, don't you?

Php pages are build by smarty templates, so i though also, as second chance, to lay hands on these files, but really I should say to don't know what I'm to do, so... what else?
Thanks and, of course, any other suggestion is welcome.
Cheers,