Where can I download the patches?

For the love of God man! Install the patches asap.
It will spare you from annoying bugs and from hundreds and hundreds of ridiculous threads.
Download the Offical Patch for Shadows of Amn (only!) or the official one for Throne of Bhaal (SoA + ToB).
Now do yourself another good thing and download the (unofficial) bugfixes for these games at Baldurdash (do it!).

Too confusing? You can find an in-depth list below. The mention of mods was added for completeness sake: disregard that information if you're not familiar with it. Most mods can be found on the Infinity Engine Modlist, graciously provided by the PPG. I strongly advise reading the readme of each mod as it can have some extra information on the installation process and conflicts with other mods.

If you have BG2: Shadows of Amn and Throne of Bhaal installed, then this is the Basic Installation Order:
  1. SoA
  2. ToB
  3. ToB official patch
  4. ToB Baldurdash Bugfixes
  5. dialog.tlk overwriting mods (-)
  6. WeiDU mods
Important: just the ToB official patch, not both!

However, if you have only Shadows of Amn, then this is the Basic Installation Order:
  1. SoA
  2. SoA official patch
  3. SoA Baldurdash Bugfixes
  4. dialog.tlk overwriting mods (-)
  5. WeiDU mods