For Win XP Pro
To enable "PlainTextPassword" connections: 

Windows XP Professional has menu options (below) that should be used to enable plain text passwords for SMB servers. The Windows XP Home edition requires manual addition of this "xp.reg" registry key. 

Start -> Programs -> Administrative Tools 
We have seen some Windows XP systems that did not have Administrative Tools on the Programs menu. If it is not there do: 
Start -> Settings -> Control Panel -> Administrative Tools 
or 
Start -> Control Panel -> Performance and Maintenance -> Administrative Tools 
On the Administrative Tools Folder, double-click Local Security Policy. 
On the Security Setting folder, click the plus sign next to Local Policies +to expand it. 
Double-click Security Options. 
Scroll down to near the bottom of the list. 
Double-click -> Microsoft network client: Send unencrypted passwords to connect to third-party SMB servers 
Click the Enabled radio button. 
Click OK 
Close the Local Security Settings Window 
Shut down Windows XP and reboot. 
After rebooting, use the above procedure to check that Microsoft network client: Send unencrypted passwords to connect to third-party SMB servers shows the Local Security Setting set to Enabled. 
For Win XP Home
Use regedt32 and go to: 

 HK_LOCAL_Machine
 system
 CurrentControlSet
 Services
 Lan man workstations
 Parameters
  > Enable plain text password --> to 1

  otherwise  RtClick  New 
        dword_value
        EnablePlainTextPassword   setvalue to 1