The problem you'll run into is with any hardware-specific kexts for your new computer. I can't tell you if those problems exist, but it is a potential problem. The only way to know is to boot up with the old drive and new computer. If you can boot the old one in Target Disk Mode you should be able to connect it to the new one by a Firewire cable. Then turn on the new computer while holding down the Option key and when the old drive shows up on your screen, use the arrow keys to select it, then hit Return to boot from it. If it won't boot, then you could use Migration Assistant with the FW drive still connected.