Components Upgrade for Video Editing

I am wanting to upgrade my Dell XPS 420 to a high performance video editing system. I'm very new to hardware upgrades and have a couple questions.

RAM:
The 420 supports up to 8GB of DDR2 800 RAM and I want it upgraded to the max. I did some searching at Newegg and came up with this page that lists all the available RAM that should be supported by the 420. I'm leaning toward the A-DATA for the sole reason that has gotten many positive reviews. If you have any other recommendations please let me know.

Hard drive:
My XPS 420 already has one RAID 0 1TB (2x500) hard drive. But have been told may times to never have the OS/software and videos on the same drive. So, I have been looking for a high performance HD to store Windows and my apps on. Then came across the 10,000 RPM WD VelociRaptor. Now, currently my RAID 0 is drive C. Will I need to reassign drive letters to install Windows on the new drive, if yes how is this done? What else needs to be done to successfully transfer Windows to a new drive?

BluRay Drive:
I'm also thinking about upgrading my DVD drive to a BluRay drive. Is the width of these drives universal so BluRay would correctly fit in the old DVD slot?

Operating System:
I'm also wanting to upgrade from Vista to 7. But have heard that 7 has issues with e-sata drives, is this true?

Is there any certain order these should be done in? Should I attempt to upgrade it myself or have a more experienced person do it? If you have any suggestions please let me know. Thanks!