What quad-core cpu have you got that only benches 1000 in geekbench?! That's pretty sluggish.
Tonymac is a great resource for what you are trying to do, there is also insanelymac.com.
I have converted quite a few myself, if you want any help or advise you can pm me if you like.
You can install both os's onto the one hdd, but you'd need to partition it first. You can do so from within the installer if you go to tools - disk utility