OK, thanks guys, you gave me what I needed. It was the "guest" option that was causing the problem. It would appear that the kernal portion of cifs has changed and no longer allows the guest option, even though the manual hasn't caught up yet. I can use the user/password option with any password and the Windows share will allow guest access if there is no matching user/password account (if the Windows share is set ulp to allow that option).
So, to sumerize: don't use the -o guest opton. Use -o user=anyname,pass=anything,vers=x.x
And I now understand vers=x.x. It is the protocol version, and yes, for XP I would use vers=1.0.
I don't know why sometimes I got the host down error (112) and other times I got 'Invalid argument' for the same command. But I am glad that it is working now. Syntax is everything!
Again, thanks to all who responed. Your help was great. And I can now access my Windows shares.