External HD or, Partition Existing WD?

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I have, once again, been considering trying Linux. I am not a computer builder, yet, so am ferreting my way through this site. In reading a post reply to me from Faulkner132, concerning method of downloading the ISO for ubuntu, it was suggested that I post my partitioning question here.

My quandry is this: As I just replaced my HD, a seagate which failed, with a WD 250 GB Internal, I started to think that for my trial of Linux it might be better to purchase an external HD for my purpose rather than take a chance of screwing up my new Drive and losing what I have just replaced, again.

So, I checked my computer and found that I have, I think, Firewire (DeviceControlFireWire-Adobe Premier Plugin) and SATA (PlugIn Sata-pin and PlugIn Sata-ENU.dll) Does this look correct for having the two? I then read the stickie, "A Guide To Sata". Now I would request, from you folks, opinions on whether I should partition my WD Drive (230 GB Free) or, buy an external HD (WD, Maxtor, other?) and go from. I have, I believe, RAID on my computer, a Sony Vaio VGC RA840G, though I doubt that that would have anything to do with it as I am trying to separate Windows from Linux. Or, am I concerned needlessly and just go ahead and partition my HD on the Sony? I was reading that Linux install will partition my HD if I install correctly. But, have no idea about anything Linux and am facing a bit of trepidation. Never been afraid to give it a go though.

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Just give me a shout when someone has an answer or recommendation. I am, after all, a very patient person!