From ExReport 3.011 and onwards, ExReport can use up to 4gb of ram on Windows 64bit in addition to any memory allocated to the operating system and other applications.
Ideally a Windows 7 64bit workstation should have 8-12gb of memory minimum, 4 for the operating system and 4 for the queries.
The CPU minimum specification should be quad core or multiples thereof to provide maximum functionality and speed.