[Samba] Windows XP connects as guest instead of letting me choose the username / password

[Sebastian]

Hi,

I suspect this is more of a WinXP issue, but since it drives me mad, 
I'll ask anyway.

What I want:

In Windows XP network neighborhood, select my samba server, select one 
of the shares, then have a dialog asking me for the respective 
Samba-username & -password to access the share.

What I get:

I get a dialog with the username "Guest", greyed out, asking me for a 
password.

My question:

WHY does XP always assume I want to access the share as "Guest"? Can I 
disable this behavior somehow?

What I tried:

- set requiresignorseal = 0 in XP registry
- set security to SHARE in smb.conf
- disabled XP simple file sharing
- registered the username/password combo with samba using smbpasswd

Has anyone had this problem before? Any suggestions? Thank you very much,

Sebastian