Given how much and how often things have changed since 2003 was released, it would be worth checking both the Samba config and Windows NTLM level.
Samba is in the config file above and Windows can be found with:
start -> run -> gpedit.msc -> Computer Configuration -> Windows Settings -> Security Settings -> Local Policies -> Security Options.
Network Security: LAN Manager Authentication Level.
Edit: Just be aware changing the Pi end may break your working connections
Need Pi spray - these things are breeding in my house...