This is what I did during my install:
Install TBC from the 4CDs, have your CD key ready - on the sleeve of Disk#1. The registration done in a pop-up window during install.
Once complete, run WOW from launcher like usual
On login, WOW will say "downloading update" - but actually downloading the patch download program
Once "downloading update" completes just hit the "Restart" button and WOW will check for WoW-2.0.0-to-2.0.3-enUS-Win-patch in C:\Program Files\World of Warcraft\Patches folder. If present this patch will immediately start updating your game to 2.0.3
Back to login screen.
Login again. Again, game will say "downloading update" - actually downloading the downloader for WoW-2.0.3.6299-to-2.0.5.6320-enUS-patch.
Once "downloading update" completes, click "Restart" and WOW will start downloading the patch WoW-2.0.3.6299-to-2.0.5.6320-enUS-patch.exe. Small file (2.8Mb) but takes a while, thanks to the sheer number of users and TMnub

Took me 30 mins.
Once the 2.0.5 patch is applied, you are all set. Simple and (almost) painless
Welcome to outland!
Note: Seems like the patch resets a lot of your options to defaults and wipes the /Addon folder so you will have to reset these.
I expected the update to FUBAR so I backed up the whole WOW folder at each point in a USB HD. Software development instincts

But no problems at all, so all credit to Blizzard.
This post has been edited by limsk: Jan 18 2007, 01:47 PM