Willcrabb, I am assuming u downloaded the zipped file successfully with the 1.1 client. First of all, backup your bin folder before doing anything, just copy it and save it as bin-old. or similar. once you have done this, open bin, then delete everything apart from the "version" file. so delete the natives folder, minecraft.jar etc....
After this, just extract the contents of the zipped folder into the bin.
An important thing to remember is, make sure the directory is the right one. For example. using win7, it could be in: Users/Willcrabb/appdata/roaming/.minecraft.
The appdata folder should be hidden. And the "Willcrabb" is your profile name or w/e.
Just run the .exe and it should work.