You do not have to use separate partitions.
First install everything
to the ssd disk. Also format the hdd as ext3 (or your preferred filesystem), but leave it empty for now.
I think you will have to do this from a live distro to avoid moving files that are in use.
Create a directory on the empty hdd called home
. Now copy everything from the original home to the home directory on the new hard disk. Now delete your original home directory and then create a softlink to the new home directory (as root). Something like this if hdb1 is your hard disk:
ln -s /media/hdb1/home /home
I'm not sure if you'll run into problems here because this is on a live distro, but I think that softlink should work on the actual installed linux. Somebody correct me if I'm wrong.
That creates a pointer that will keep everything working the way it is supposed to because you didn't change any file paths, just moved things around on the disks. You should be able to repeat this procedure for other directories such as /var and /tmp etc.