Replacing a HD in a PB isn't that hard.  I would go to 
iFixIt formerly PBFixIt.com for guides and parts (or go else ware), and search these forums for threads like 
 and [URL=https://forums.macrumors.com/threads/179602/[/URL] and [URL=https://forums.macrumors.com/threads/132599/] this one.
Instead of a drive enclosure you can also get a cheap 
 USB to IDE  connector for about $20 U.S.  I don't trust TigerDriect because the denied a rebate that I know I did correctly.  Search for Cables Unlimited USB 2.0 to IDE  Cable with Power Adapter.  I used one to transfer data from my busted iBook.
Connect the new drive to your enclosure or the USB adaptor and then have at cloning.  
Generally I zero out all new drives then partition (set number and size to what ever size you want), rename, etc...
Then I use 
Carbon Copy Cloner, but others like 
 Super Duper.  
SilverKeeper is another option.  I have used SK, but I don't like it very much.  CCC is not free, but it's demo is limitless.  It costs 5$ U.S. SK is free.  SuperDuper is nearly $30.0 U.s. Always check your clones, and always follow the directions.
Before you clone, I recommend running, some sort of system health utility, or run the standard scripts in terminal.
The utilities I recommend using (use one not all) are
ONYX or 
Main Menu.  These are good maintenance utilities. 
MacSweeper  is for 10.2 and before.  I use Main Menu, but ONYX used to be my favorite.  They also allow access to other features of OSX that you might not easily find through the normal GUI if at all.  Currently MainMenu is being updated to both work with the latest Tiger update, and massive improvements and additions for sale as a pay app.  For now it's free.
Lastly clone the drive.  It's easy.
Carbon Copy Cloner, but others like 
 Super Duper.  
SilverKeeper is another option.  I have used SK, but I don't like it very much.  CCC is not free, but it's demo is limitless- so it is free for those who see no value in it.  It costs 5$ U.S. SK is free.  SuperDuper is nearly $30.0 U.s. Always check your clones, and always follow the directions.  
Check you clones!