The main URL for current Eurobook is http://www.geardown.de/EUbooking/, which you need to replace with http://vatbook.euroutepro.com/atc/. That's all. The interface is identical, no other changes have to be made.
For example, if you use Romain Riviere's phpBooking, in the file atc.php you will find a line that says:
# Eurobook communication
$url = "http://www.geardown.de/EUbooking/delete.asp?Local_URL=http://www.pl-vacc.org/pol3/admin/eu_del.php&EU_ID=$euid&Local_ID=$localid";
All you have to do is replace it with:
# VATBOOK communication
$url = "http://vatbook.euroutepro.com/atc/delete.asp?Local_URL=http://www.pl-vacc.org/pol3/admin/eu_del.php&EU_ID=$euid&Local_ID=$localid";
Please note the part about pl-vacc.org URL in the above quote is of course specific to PL-VACC. Your URL will be slightly different, but you only need to replace the "www.geardown.de/eubooking" part with "vatbook.euroutepro.com/atc". Also note that this URL will typically exist in your software in more than one place, and you need to replace all occurences.