How to reset Lotus Notes user password ?

It's my understanding that you can no longer reset the password on the user.id file and send that to them.
You can either use the original user.id file (if you still have it) which hopefully has a generic password on it. Or you must go through the Password Recovery process.

If you registered a user with the same name then they will automatically get a '1' behind everything.
ie. John Smith = jsmith if you created again it will be jsmith1

Hence it's just creating a new user, no attributes such as ACL's etc would carry accross.

Someone else may no a way to reset passwords on user id's but our Notes admin always insisted it wasn't possible.

You need to have figured this out before you loose the password. On older versions of Notes you could have had an reset facility pre-configured on the ID file. This is accessed in the Domino Administrator client.

In newer version (though 8 or 8.5, not sure which off the top of my head) there is an ID vault which keeps copies of the ID files as well as allowing users to download them and have their passwords changed centrally. This is also accessed in the Admin client, but also needs to have been set up when you configured the user.
http://www-10.lotus.com/ldd/dominowiki.nsf/dx/12162008022843PMNEKQT7.htm
http://www.scribd.com/doc/10043973/Step-by-Step-Instruction-How-to-Enable-ID-Vault-in-Domino-8x

If you've not done either of these, you can create a new ID, but make sure you delete the user from the directory first (move it somewhere else so you can get it back if necessary). You can then create a new user with the same name (which will work for ACL etc), but the certificates will be different, and the user will loose any other certificates they have in their ID file (though they may be able to get a copy back if they've shared them with someone else).

Recreating the id throws away his current public key and private key.  This means that if If this user uses encryption, he loses acces to the encrypted items.

@Andoss: Please read up on Domino Administration.  Your comments are a dangerous mix of true and false.

Possible options:
1. recover old ID from a backup for which a password is known, and use that in the users notes client.  If the user has been recertified the notes client will pick up the new certificate from the server as soon as the client opens a db on the server.
2. If password recovery process was setup, use that procedure
3. if you MUST recover the password and you have lots of time on your hands there is a password cracking tool from Elcomsoft

For the future: read up on ID vault feature of Domino 8.5.  Google for ID vault and Gabriella Davis for an excellent presentation. Implement it.  While your at it, closely study the Domino Administration help file.  You will be amazed at the options Domino offers you out of the box.  For trying out new options, consider setting up a trial version of Domino on a separate machine (can be VM).  Especialaly in a migration, TEST!  If the test server uses your existing certifier be very very very careful that the two server never see each other on the network.  You are better off creating a new server with a new domain and new certifier and new test users.  This will mean some translating of the tested procedure, but stops possible errors due to the test environment replicating unwanted changes back into the production environment.  

thanks guys for the suggestion, FYI the scenario is like this:

My boss wants to use Lotus Notes for a side project, long time ago i set it up but i also forgot what's the account password, The user ID is located on the shared network drive but we both forgot what the password is.

I need to generate the new .ID file and place it on the file server, is there any way to accomplish this without having to reset the Database ACL and groups ? --> in case anyone wondering what's going on :-)

@larsberntrop - can you please point out the 'dangerous false comments' i made?
You practically posted the same thing just expanded on it?

Which one ? i also confused here :-|

yes i didn't dare to delete any username in the Domino system, only delete it when the user is no longer with us anymore longer than 1 month.

thanks man for the explanation and the guide.