How to write to a winxp partition file from the Linux partition?

[joe]

On my dual boot system, while logged into Linux, I can cd /mnt/windows and
view all the files on the windows partition, but they are all r-xr-xr-x and
even as root, I cannot copy a file or write to a file or change file
permissions on a file in the winxp partition.  Why is that?  Surely there must
be some way to overcome this barrier.  What's the secret?