I note there are no share names listed on the output of your smbclient -L //<WinXP server name> command. When I do this from my FC5 box, I see all the printer and disk shares that I have defined on our XinXP box. Other than that, my output is the same as yours, without the "NT_STATUS_OK" status message. File Browser (Nautilus 2.14.0) successfully connects to the WinXP box disk shares.
I'm just guessing here, but when you created your Win shares, did you enable "Share this folder" on the "Sharing" tab properties of your shared folder? Can you verify sharing from another Win box?
HTH,
Jon