How to create a new tarball?

Hello folks,

i want to create a new tarball from the nios2-linux stuff just like the

"nios2-linux-20100621.tar" file. Because after a new installation the ./update script wich pulls all git-repositorys always takes a long time to compleete due to many changes. (I have to use http for update).

I have already tryed to clone the repositorys with

git clone --bare /repro.git /rarball/something.git

but when i try to execute the checkout script it says:

fatal: This operation must be run in a work tree

I'am going to have a tarball, where all subdirectorys only containing the hidden ".git" directory (just like in "nios2-linux-20100621.tar").

Any git expert out there???