Restrict USERs install by GPO

Hi everybody,
I am having 40 windows2000 clients ans 20 XP clients.(60 users),My server is Windows 2000server.
Now i want to configure 30 users should not have a installation permissions on their systems,but 20 users have a installation rights.all the systems accept software installations depends the user rights.
how can I configure these setup by using GPO.? should i create a 2 or more GPO? please help me.

thanks in advance.