Can I install Xubuntu on a different internal drive to the boot drive?

Hi All

I successfully installed Xubuntu on an old (2006) MacBook today, with zero experience of Linux... and I am delighted. it also seems to be running a lot faster than the version of OSx I have on that machine - despite only having 1MB RAM! I really am pleased, I mean incredibly pleased!

So, this has given me food for thought and I am considering installing Xubuntu (or even full Ubuntu - not sure) on my main MacBookPro machine... but on a separate HDD which I have on the machine as a replacement for the optical drive I rarely used.

So my questions to you good folk are these;

1 - Can I install Xubuntu on a totally different HDD (but located inside my MacbookPro) and use the same software to select a dual boot? (rEFIned)
2 - Do you suggest I install Xubuntu (which I installed today on the old Macbook) or should I install Ubuntu?
3 - Are there other 'boot' alternatives to dual boot that I may not be aware of? (cannot see that there are, but I guess I should ask nonetheless)

Your thoughts would be appreciated. Thanks all!