This one does 50Hz PAL:
http://www.synchrotech.com/product-1...-firewire.html
If you could tell us what kind of Mac you're running, we may be able to point you in the right direction -- right now, we don't know if you need an external device like the one linked above for use with a desktop like an iMac, or if you're running a desktop Mac with PCI slots and could use a PCI card for capture.