So long as you use a newish card it doesnt really matter what you buy. I believe some fx are rendered faster in some packages - after effects and the newest premier, but the speedup is not huge ( i think).
As for monitors, 2 (or more) rules for editing. I currently use 4 and it rules, but 2 is miles better than one.
Most g cards can support 2 monitors, check when buying. If you want to get carried away like me keep an eye on e bay for an old pci quad head matrox, not 3 d but fine for everything except games.
I run the monitor I use for preview with a gforce 7400 (i think) as this takes some load off the cpus when previewing in the editor.
My order of importance for an editing set up (and i am no expert) would be...
1. Reliability - no overclocking or fancy tweaks.
2. A comfy chair - it's my second home.
3. Coffee, fags - I am weak.
4. 2 or more monitors - more space, faster better work.
5. A decent sound monitoring system - NOT just manky pc speakers. I use JBL control ones with a sub driven, by a decent hifi amp. Sound matters.
5. Fastest cpu you can afford - has to be dual core.
6. Fast drives - go for a really fast c drive (raptor), and a seperate fat drive for video.
7. RAM - the more you have the smoother things get, over 4 gig may be overkill.
8. More coffee.
9. Fast g card (i dont play games)
10. A mac -
__________________
Lowering the tone of video since 2004.
www.zaskarfilms.com You tube channel 'zaskarfilms'
JVC DV5001e (big cam), Sony PC6E (tiny cam), Vinten pro5, PAG light, SM58, Sony ECM50, Sony C-76, 0.5x convertors for sony, Rode video mic, Vegas 7.