Hi, I don't think doing a chroot on the Debian Sid install will work because you will still have access
only to the binaries available on your Sid partition. Anyway, from what I read on the
Debian Wiki you need the
firmware-ralink package installed. Have you tried installing it on Sid and see if it works?
EDIT: Another possibility if you want/need to compile the drivers on the chrooted Debian Sid, is to mount it, copy the /etc/resolv.conf file from your Squeeze partition into your Sid partition, chroot your Sid partition, and then install
build-essential (with apt-get or aptitude; you could also install the firmware-ralink package this way).
Regards.