Empty your internal hdd, working from a network drive is not a good idea.
Get more internal drives. That is the best way to edit video.
Also you can render the timeline to get better palyback.
Also, if, after following Ann's suggestions, PrE is still having issues with the AVCHD material, it might be time to look into a new CPU. That AMD Quad-core is going to be stressed. First, a Quad-core CPU is the bare minimum for working with AVCHD material (a fast i7 will be much better), and also AMD CPU's lack the optimization for running many Adobe programs, that an Intel CPU will offer.
>2 TB Network HDD
No current version of Premiere works properly, if at all, over a network
-you may NOT "map" your My Documents folder to a network drive
-you MUST give all users administrator accounts to use Premiere
-you MAY also need to... http://forums.adobe.com/thread/969395
-a work around, of sorts http://forums.adobe.com/thread/957523
-and not on a "domain" http://forums.adobe.com/thread/858977
-also PreEl see #5 http://forums.adobe.com/thread/1017199
-more PreEl problem http://forums.adobe.com/thread/975117
Thanks for the responses. I was afraid that's what the problem was, but was hoping there was something I could do about it.
>hoping there was something I could do about it
There is... buy a second 7200rpm internal hard drive for all data files... Or, use an eSata or USB3 external
External eSata or USB3 are both fast enough for video editing... eSata is better - http://forums.adobe.com/thread/1117813