In a recent Famitsu interview
http://www.famitsu.com/interview/article/2007/02/14/668,1171444185,67084,0,0.html ...
Namco head developers talked about the future of the franchise and the porting process of Tekken 5: Dark Resurrection from Arcade to PS3.
It took them roughly 2 months, they didn't do anything to change it aside from altering the backgrounds to fit in HD resolutions.
They mentioned that Tekken won't be going online anytime soon, but that doesn't mean they aren't looking into putting another type of fighting game online to test things out.
Tekken 6 will look MUCH, MUCH better than any Tekken before.
(MarkMan's note: Tekken 6 video shown at E3 has nothing to do with T6, it was just a last minute video done at request of Sony for the show, they used the existing DR graphics engine for it... as told to me by the Tekken: DR producer himself at E3... end note.)
Also, the devs mentioned that
it is possible to update/patch Tekken 5: DR on the PS3. While there are no plans to do this anytime soon, it is definately something that can be done.