Impossible to connect to shared folders from Windows XP to Mac OS X 10.10
Releasing Mac OS X Yosemite, Apple has updated the SMB protocol to version 3, as documented here. Windows XP, on his side, works almost certainly with the SMB 1 protocol, because the upgrade to version 2 has been done on Windows Vista, as mentioned here. The backward compatibility allows SMB 3 to connect to previous versions, but not viceversa.
This issue can be solved using Samba, a free and open source implementation of the SMB protocol that assures full compatibility between different operative systems.
It is possible to install and manage Samba on Mac OS installing SMBUp.