I've heard that samba stores passwords in a less safe way than the normal linux passwords.
Is this true? If yes, what can I do about it?
Samba can authenticate in a number of ways but in a stand-alone situation I expect is most commonly configured to authenticate against hashes of passwords, the hashes being stored in /etc/passwd or (more usually nowadays) in the shadow password file.
The person who you heard this from may have been confusing storage with transmission.
I recall (but cant find the references right now) that the main factor causing this issue was the way Windows clients authenticate. They require the server to know the password. This is unlike other authentication systems where the server only needs a hash or a public key and where therefore it is not possible to retrieve a password (or equivalent login credentials) from data stored on the server.
Samba can also authenticate against Kerberos or LDAP servers. So there is plenty of scope for setting up a secure system.
The Register has an interesting article on NTLMV2.
Actually NTLMV2 doesnt require the authenticating server to know the password - according to this Miicrosoft article.