Greeting guys! So I've had a few requests to do a 1.3.2 downgrade tutorial, so here it is! :D
1.First: Go to your start menu and type %appdata% this will bring you to a big folder.
2.Once there, select .minecraft and then go to the bin folder.
3.Next, delete the minecraft.jar if you have mods installed for 1.4 this will obviously delete them.
4.Download the 1.3.2 jar from this link.
[NOTE] I did not create this link and no illegal action is intended, this is a link I found.
5.Now go to the folder of which the new minecraft.jar was downloaded to.
In my case /Downloads
6.Move the new minecraft.jar to the bin folder and close down all the folders you don't need.
7.Finally start up minecraft and you have successfully downloaded to 1.3.2!
I can't get on minecraft due to problems with me and mojang so I haven't tried 1.4 yet, but i've heard there are bugs in multiplayer e.t.c. so hopefully this helps!

-SkinFTW