Problem editing user roles

I’m new to blogging, new to WordPress.
Trying to build a website for a comunity (using wordpress 2.8.2) and I’m still testing it.

The site does not have any important content (only some I added fot testing purposes) and I recently messed up the user roles using Role Manager.
For a while, I didn’t have any admin user, but I solved that by deleting the *_usermeta and *_options tables.
I than created a new admin user and was able to log in as administrator.
I tried to restore the site by importing from a backup file from the previous day.
As expected, it asked me about the 4 different users i had at that time.

The problem:
I cannot assign any roles to users. I can create new users but they’re still unchangeable and their role is always set to “None”.
When I try to change their roles it tells me changes have been applied, but all users remain unchanged. Under “Role” in the “Users & Authors” section they all read: “None” (except the new one, which is “Administrator”.

Something else (don’t know if this is normal or not): all users have unchangeable names.

Any suggestions?