Just 'unzip' the .jar file and delete all the .class files and you will be left with the default textures.
I personally use 7-zip for this purpose.
I might actually have a .zip with just the defaults in it lying about here somewhere... *rummages* default.zip
That should be the latest textures from the 1.4.7 pre-release.
The_Fool76 is correct on how to do it. I would suggest however checking out the "All Inclusive Texture Guide" it has a section that covers getting files for mac and pc so that you are covered with detail. Check out that section here.
i would also like a link to the latest version of the default texture pack because i replaced it accidentally replaced it with with some random texture for like two blocks so now every thing is just a block that says "missing texture" so ive been forced to u a VERY CRAPPY ONE until i get the default one back. please help