You can do it during the install process by selecting "something else" when it asks if you want to install, setup dual boot, etc.
Identify your SSD as the / partition, and some partition on your internal drive as /home. If you are re-importing a /home from another system, be very careful with the "format?" option.
You can also NOT specify anything special, just a / and swap and bootloader and then go back after first boot and set up the /home. This is handy if you are using software raid, etc. or you're re-using a /home from another system. Simply run the
blkid program, get the UUID of the file system, and make an appropriate entry in
/etc/fstab. Boot from a livecd, move any files you want to keep from the first boot in the current /home to the partition where /home will be, empty /home, and reboot. During the boot process, the /etc/fstab will be read, and /home will be the partition/raid device/whtever you specified.
darkstar ~ # blkid
/dev/sda1: UUID="ba64b205-aae8-4538-a2f2-a420ab9ef2f3" TYPE="ext4" PARTUUID="d46cf327-01"
/dev/sda5: UUID="e351dfc1-ca8c-45e6-a798-709b6bf70ef0" TYPE="swap" PARTUUID="d46cf327-05"
/dev/sdb1: UUID="80b0bf23-7ba6-482d-98c5-febc1b607e7a" TYPE="ext4" PARTUUID="000a5f65-01"
So if I want /dev/sdb1 to be /home I would add the following to /etc/fstab
UUID=80b0bf23-7ba6-482d-98c5-febc1b607e7a /home ext4 errors=remount-ro 0 1