Linksys wrt54g units are broadcom based chips, Atheros chips, which is what the new buffalos are based on, are entirely different. And for the record, the DDNS bug effected all dd-wrt builds, even the newer builds for the wrt54g, its a system wide bug, not platform dependent.
There are community builds of dd-wrt in which DDNS works, but as i said, you'd do better sticking with the buffalo dd-wrt builds until you have more understanding of what you are doing and how the buffalo dd-wrt builds vs. the community builds work. Example, if you flash a community build, you not only void your warranty, unless you know how to flash back and forth using TFTP, you'll be stuck with a community build with no hopes of being able to flash back to buffalo dd-wrt builds. Google all this info, its there.