Its not the Firewire thats the problem (Assuming you captured in DV-AVI format). Its more likely to be the settings you used in encoding your edited video to DVD compliant MPEG2.
The best setting for this is to set your Video bit rate to 8000Kpbs. This will get you about an hour of video onto a standard DVD.
Let us know what software you are using if you need any additional assistance.
Meantime, good luck
COMPAQ something or other with 500Gb Boot Disk, 1Tb external Firewire Disk, 4Gb Memory and a super duper sound card, 19" TFT Monitor etc etc etc
Sony TRV33e : Sony TRV310e : Canon XM2
Sony Vegas Studio editions to v11
Remember, there is always more to learn than there is to teach.