Joseph,
The segmentation is easy - all servers can keep their current IP addresses - but you have to ask more specific questions of the cutsomer:-
1) how many servers per site
2) how many users per site
3) Are the servers & users in different vlans's/ip subnets
4) Do you have specific mgnt IP addresses for network management per site
5) Do you have specific team ip addresses for servers per site
You could easly subnet - using the above as an indication:-
Paris - 172.16.0.0/22 - 1000 IP avail
St Ouen - 172.16.64.0/22 - 1000 IP avail
Auvervillers - 172.16.200.0/22 - 1000 IP avail
leaving plenty of room for expansion and new sites if nessary.
HTH>