dd if=/dev/sda7 of=/dev/sda1 bs=4096 notrunc
that should work, but I've never tried it and if something goes wrong /dev/sda1 is toast. You would have to reload onto sda1. dd is very powerful but very dangerous if done incorrectly. Make sure also both of those partitions are unmounted before you do that command. If you use lilo you will have to fix /etc/lilo.conf as appropriate and rerun lilo.