Vista use different security protocol. When using Vista to access shared folder on XP machine, I keep getting access error.

Here’s the solution to get Vista to access shared folder on XP

Windows Vista uses NTLMv2 only by default, you can change it to use NTLMv2 or the old NTLM as used by XP:
a) Load Secpol.msc
b) Expand Local Policies, Security Policies
c) Change ‘Network Security: LAN Manager authentication’ from ‘Send NTMLv2 response only’ to ‘use NTLMv2 session security if negotiated’.
d) Close secpol.msc

If Using Home edition, then you will not have Secpol.msc. Load Regedit, goto HKLM\System\Control\Lsa and change LmCompatibility level from 3 to 1.