Upgrading CIFS protocol on XP to work with 2008 R2?

I was speaking with a colleague about our migration to 2008 R2 on one of our
servers and the affects it had with our XP clients on the network. He
mentioned that he was experiencing extremely slow read and write times on his
XP machines and that he had to make some registry entries on the 2008 R2
server so it would allow both the older and newer versions of CIFS to be used.

I've been looking and can't seem to find any information that specifically
addresses this issue.

Would anyone be able to point me in the right direction?

Should I be searching more for info regarding upgrading networking protocols
on XP machines rather than hacking the server?

Thank you.