I never had a speed problem with my iBook G4. Sure, YouTube isn't the greatest, but it's very usable. And you shouldn't be expecting to buy new software for any machine that old.
A $600 MBP, even one of the Rev. A's, should be highly suspect. It's hard to even find MacBooks that low in price.
They were going for $900-$1000 before the last rev. It's not all that suspect.
Why would you buy a Powerbook to run Panther? You're not going to be able to run any software from the last 3-4 years. In addition, you're not going to be able to use most of the web. And the battery life on a machine that old is going to be pretty poor, so right away you're going to be springing for a new battery.
And, because it sounds like a titanium, you're going to be dealing with the machine physically breaking down (which seems to have already started), and the hinges breaking.
You might as well be taking your money, putting it in a pile and burning it, and then paying rent to use the fire pit you just threw your money into.
Also don't plan on watching YouTube on it... It's simply not fast enough. I have a friend with an 800 mhz iBook, and YouTube simply did not work at all for him. Completely unplayable.
Again, save your money for an Intel. They aren't too much more for a 13" Macbook, which despite the smaller screen size, will be much faster for your needs.