From the Instant 4.1 Online user guide:
http://www.arubanetworks.com/techdocs/Instant_41_WebHelp/InstantWebHelp.htm#UG_files/DHCP_conf/DHCP Config.htm
"Configuring the Default DHCP Scope for Client IP Assignment
The DHCP server is a built-in server, used for networks in which clients are assigned IP address by the Virtual Controller. You can customize the DHCP pool subnet and address range to provide simultaneous access to more number of clients. The largest address pool supported is 2048. The default size of the IP address pool is 512."