Spread /home partition over two drives?

It seems like you need a bit more information on the Linux directory system: You have one root directory / on your system. And this is where you have a number of folders like /home, /dev, /usr, /etc and so on. Some of the folders really exist on the disk, like home, usr and etc, but some are only virtual like proc or dev and contain temporary system/process/device info/represent them.

Now you have to understand that EVERY machine has this equal basic structure, independent of the underlying partitions. Every partition you mount gets placed into this one file system tree and bind to one specific directory. So e.g. your /home directory points to the partition sdb1 (which is represented by /dev/sdb1 by the way) while your /boot folder is located at sda1 and the rest of / is in sda2.
You can also just create a new folder like ~/data and bind the partition to this new folder.

So for your system you can say the following:

The only two partitions you need are / (the tree root) and swap (which does not get included into the tree). Then all data in any real directory under / would be stored in the root partition.
What you can do now is to take specific directories out of the root partition / and assign their own partition to them. Commonly you do this for /home and sometimes for /boot.

It is easy to do this at install time (select "do something else" when it ask whether it should install instead/alongside other OS and do the partitioning manually), but a bit more difficult to change it later, as you have to manually move the contents from the old directory to the new partition before you bind it. But it is of course possible and - this is the big advantage of this directory system - applications will not see any changes, as they still can access their files as before, because the path (e.g. /home/myusername/.mygame/hiscore) to all files stayed the same.

So what do you exactly want to do now and on which topic do you need further help?

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