The perms of a mounted filesystem can be set for the whole filesystem, but more usually for the individual directories/files on the filesystem (vfat however must be mounted as a particular user as it doesn't support permissions properly)
However if you were root when you copied files to the card you most probably made all the directories owned by root, therefore zaurus user won't be able to create files.
cd to /mnt/card and run
chown -R zaurus.qpe ./
to give zaurus ownership of all files and directories (this may take some time)
Most of the ext2 drivers for windows that I tried before I changed to reiserfs were read-only by default - some of them had options that allowed read-write but some of them didn't. Check the options available for your driver (beware some ofthe ones I tried were maga-dodgy and hosed my filesystems)