The Sanyo relay that you mention is going to draw 40mA at 5 V. This defenitley will need a buffer.

You can use a PNP transistor like the BC557 or equivalent that can handle this kind of current. Drive the Base of the transistor through a 2.2K resistor from the Port pin and connect the emitter to 5V . Use a 10K pull from the base of transistor to 5V.

Your relay WITH the freewheel diode must be connected between the collector and ground. And this relay will come ON when the port pin is driven low by your code.

Actually this configuration was posted here by Michael J Karas and has been found to work OK.

Raghu