Unless you are having other problems that might suggest a different cause, I would be suspicious of the cable first.
The simplest test will be to try a known-working cable. To test further, you can also try connecting your camera to a different Mac or connecting a different FW device to your Mac.
If you, your family, or friends do not have access to other Firewire cables or devices for testing, and if you bought locally, you can take your MBP, the cable you bought, and your camera to your local retailer for testing. Even if you bought elsewhere, a local retailer might be willing to test your cable and camera on a different computer or sell you a different cable that you can test at the store to be certain it works before you leave .
If you are interested in using adapters with your existing (and known to be working) FW400 cables, here are a couple from which to choose. There are others, but these have worked Mac users I know:
http://www.sonnettech.com/product/fw_adapter.html
http://tinyurl.com/cgll7o
EZ Jim
G5 DP 1.8GHz w/Mac OS X (10.5.7) PowerBook 1.67GHz (10.4.11) iBookSE 366MHz (10.3.9) External iSight