-codycartoon
I think I have an answer for you. You machine is plenty fast enough, it sounds like you have a few bottlenecks when it comes to Read/Write.
One, get a little more RAM, as much as you can with the money left over from my next suggestion:
Get an additional Hard drive - physical partition.
Yes, I know you have created logical partitions within your 80gigger, but remember, you are still limited by the platters of the 80Gig drive being accessed by one armiture. And that armiture has to continually read OS and FCP/X functions in addition to the media streaming you require. The answer is two heads (pun intended) being better than one.
Get the second drive - doesn't have to be absolutely huge - and expensive, say 40GB - go with me here, it'll make sense in a minute.
The intent here is to turn the 40 into your primary drive, the one with the user accounts, OS and Apps. Then to use the current 80GB, which is most likely a 7200RPM drive, as your "Composition HD".
Use the money left over to get as much RAM as you can.
Now, how to 'flip" the drives...
-Put the 40GB into the IDE chain, making sure it's set to 'Slave' or 'Cable Select'. Make sure it mounts on your desktop. Partition it as you wish. (I don't know why you would though)
-Get Carbon Copy Cloner.
-Clone your Primary Partition (OS, Apps, etc) to the 40GB - make sure you 'bless' the clone so that it will be bootable.
-Select the 40GB as your startup disk.
-Shut down.
-Flip the drives: Turn the 80GB to 'Slave' or 'Cable Select', and the 40GB to 'Master'.
-Boot.
-If your new 40GB does indeed boot, you're set. And now all you have to do is perform cleanup. Moving whatever you wish from the 'Slave'ed 80GB to your 40GB Primary.
-Oh, and when done, repartition the 80GB to one partition.