Hi,
this is possible and you will need to either use the RTSI bus to synchronize the two boards internally (apply a RTSI cable on the 2 RTSI internal connectors on the PCI boards) or external cabling to provide the trigger from one board to the other. The idea is that one of the 2 devices is master and the other is slave. The slave is programmed to start operations upon receiving a Trigger on a line (eg PFI0 or RTSI0) and the Master is programmed to route the start trigger onto the same line (PFI0 or RTSI0). You then start the slave before you start the master. When the master starts, it routes a start trigger on the digital line selected and the slave starts thereafter in synch.
If you are programming in LabVIEW, you may want to check out the examples that come with the Environment, under the section Hardware Input & Output>>Traditional DAQ>> and look for Triggered Waveform generation and Triggered Acquisition with DSA boards.
If you are programming your device in CVI, C++ or any other text based language, this KB helps you with the function calls:
http://digital.ni.com/public.nsf/websearch/5644685CEFD16783862568200054FA60?OpenDocument
Also be aware that the 4452 provide DELTA/SIGMA ADCs. While these ADCs provide great performances, the way they are designed introduces a delay between the time the signal is sampled and when it is available as a digital sample. This is very well documented in the following knowledgebase
http://digital.ni.com/public.nsf/websearch/F989B25FF6CA55C386256CD20056E27D?OpenDocument
AlessioD
