Well, the quickest you can get is a simple direct copy...
The process would go something like this:
1) run cfdisk or fdisk on /dev/hda to repartition the way you'd like.
2) create a filesystem of your choosing on /dev/hda1-X
3) copy everything but /mnt and /proc from /dev/hdb to /dev/hda
4) create those directories which couldn't be copied directly.
5) install a bootloader to /dev/hda
6) reboot (making sure the filesystem type which you chose in step 2 is included as a selected option compiled in the kernel)