The Titanium Powerbook would be a used or refurbished product with the best specs that the form factor has to offer..the ibook would be the 14" 1.2ghz w/Superdrive.. In comparing, there are advantages on both sides...64mb vid card for Tibook vs. 32 for ibook...faster superdrive for ibook, airport extreme for ibook, better screen for powerbook, gigabit ethernet for powerbook...etc. I do mostly audio editing and recording..light video editing..I am not going to get one of the new powerbooks because they are out of my price range. Which do you think will offer the best performance for the buck?
As a previous owner of two Tibooks, my advice is to go with the iBook. They are fairly similar, the processor would seem to offset the vram differences and the fatal flaw of the Tibook in my opinion is the case is not very durable, IMHO. However, I am sure other people had good luck with them, but I didn't. The iBook is very solid and AppleCare is cheaper for it. So that is the way that I would go.