While you can do what Tal says, you can do this easily in Wireshark. Before you capture, Capture->Options menu. Under the Capture File(s) section, enter a File name, example mycapture.pcap and then select the Multiple Files checkbox and only select Next File every 1 minute. You can option specify when you want to stop.
Wireshark then will create a new file every minute called something like mycapture_00001_20100417131441.pcap (where the first set of digits is a serial number and the second is contracted form of the date.
Simple!
