Adminitration plugin wanted

Hello all
im in very need of one particular plugin, i am looking for anything like this for 3 days now and nothing
My problem :
I am looking for a plugin that should does this things. I need to give my buddy a one whole category which he should administrates and thats it. he would not enter the category that administrates another. I want to give him acces only to the one category that he should blog on. Only the webmaster should be able to administrate whole blog. I found only one plugin which is Roles, but i cant set up the category that he should be allowed to post in.
my english is so bad so i will give you an example.

this is somewhat the category tree

News
Phones
Nokia
Motorola
Computers
Games
Hardware
My blog
Pictures

My buddy Josh can post only to News, Phones, Motorola, Nokia category
My buddy Michael can post only to News, Computers, Games, Hardware category
Me as the blogmaster can post to any category but both my buddies have restricted acces to My blog and Pictures category.

I hope everything is clear, i really appriciate any help here. Thanks in advance.