Upgrading Inspiron 640m for better video editing

Hello,

Right now it's a pretty standard setup on the inspiron 640 with 80 gig 7.2k hd inside, 1.7 core duo processor, the intel graphics card, 2gb of ram and I've just filled up a 750gb ext. usb 2.0 hd.  I'm running adobe master collection cs3 with one additional standard def monitor that's average at best and the computer struggles a little bit when I run the hi def video through the camera via the firewire 400 port to an hi def tv for a 3rd screen in the setup.

I'm looking for ways to increase the overall performance mainly to decrease the render times for buring orginal hour plus dvds and get smoother playback for the hi def video.

Tell me if I'm right in thinking it will give a nice boost with an ext. firewire 400/800/ eSata hd even without buying a firewire 800 port and upping the ram to 4gb even if like you folks say I'll only be able to use 3.25 of the ram.  You think it would give even better performance using an internal 7.2k hd than I'll get with the firewire 400 hd?  what about a suggestion for a graphics card that could give two additional monitors hopefully with hi def resolution? And the proccessor, will I get much more performance from the best one the motherboard can handle?  I'm also going to upgarde to adobe master cs4.

It's a rock solid system as is and actually buying a 2nd laptop is on the horizon for my business, I'd just like to maximze this system to help with the workflow.  Any advice would be great.