[CentOS] Problems with MySQL

Hello,

Sorry for posting this here, but i've posted in MySQL list and no one
answered.

I'm trying to set a password for a user with the command:

mysql> set password for gamito at localhost=password('blabla');

but i always get the error:
ERROR 1133 (42000): Can't find any matching row in the user table

although i'm pretty sure that the user exists.

I'm using MySQL version 4.1.20 from CentOS 4.4

This neves happened to me :(

Any help would be appreciated.

Best Regards,
AR