sudo like in Ubuntu (for Debian and other Linuxes)

I personally like the default sudo behavior of Ubuntu:
- Root login impossible
- "admin" group granted "ALL=(ALL) ALL"
- users in the "admin" group are asked for their user password (not a root password) when using sudo.

[I like it, because this way, there's no root password to be shared among several people. There may be good reasons for other opinions, too - but that shouldn't be the topic of this question.]

Now I'm trying to re-create this behavior in Debian Etch. It basically works, but there's one important difference: Debian doesn't ask for a password. It should ask for the user's password.

I edited the sudoers file to be exactly the same as in Ubuntu, and I added a user to the newly created "admin" group. What else do I have to do to get the Ubuntu behavior in Debian (and other Linuxes)?

Thanks
Chris

Answer

Problem solved itself by waiting 15 minutes...
It works now, it simply kept the password alive for 15 minutes - which is normal, but I didn't know, that it even keeps it after a logout/login. I didn't expect this at all.

Everything's working fine now, thanks for the answers! (Can/should I somehow close this question?)