i set up a dual boot system today. windows (xp) and linux (ubuntu).

it has a FAT32 partition, for sharing between the two systems, /dev/hda4, mounted at /shared.

file permissions for /shared are set such that it cannot be written to except by root. i cannot change this, even from the root account.

i can change the permissions of /dev/hda4, and if it isn't mounted, i can change the permissions of /shared.

as soon as it's mounted though, the permissions of /shared revert back to 'root only' and i cannot change them, even as root.

i've never run into this sort of thing before. what's going on?

It's because fat32 doesn't support the same attributes that a Linux file system does. Try using something like the following in /etc/fstab:
You can also give a specific user/group ownership by adding uid= & gid= options to rw,users,umask=0000 - there's more info in man fstab and man mount.