If your current hard drive is not too full you could use that same one simply by resizing your Windows partition with GParted- a guide is located here:
Note: I didn't actually have the horrific things in there happen.
With that being said... I find this to be the best setup for a hard drive:
/ about 10-15gb
swap about 2-4gb
/home everything else
I've never put /var or anything else off on its own. With this setup, everything right down to desktop configuration is maintained from install to install, just format / and mount but don't format /home.