Of everything I know about the renumbering of nvidia cards (which, trust me, isn't a lot), and looking at benchmarks (let's face it tho, benchmarks are only indicators of expected performance, not necessarily actual real world performance) the GT120 is a lesser card then the 9600 series - although not by much looking at the scores of a gt120 vs a 9600m gt.
The GT130 @ 512m *should* be superior to the 9600m gt @256m.
If you're going to really spend the money - and I mean really spend - not go cheap now and buy later, get as much machine as you can afford. I say this for some simple reasons:
1) Chances are you're going to hold onto the machine for as long as possible - this means you're going to want to make it as future proof as possible to be useable for as long as possible through software updates and upgrades. Looking at
Apple - Final Cut Studio - Tech Specs and System Requirements to use as a basis - since you are going to be using FCS and its utilities, there are certain aspects of the Color app that right now requires a 512m video card - I don't know if you'll ever use those aspects of color, but that may be a deciding factor as well - most of the other apps just refer to 256m or more for video ram (even color specifies 256m for most of its functions it would seem).
2) Upgrading a video card in a laptop is usually either EXTREMELY difficult or impossible depending on the design - this goes for the iMacs as well. on slim systems like these that uses a laptop style design, upgradeability of certain components like video cards depend on a MXM style slot existing that would accept multiple options of video cards (see:
All about MXM for more info on MXM) I don't know if Apple laptops or iMacs have this type of slot, or if it does, if it conforms to industry standards. Plus, last thing I'd want to do is to crack open an iMac case if I could avoid it...
3) Any of these systems, you're probably going to end up buying an external hard drive to connect via firewire to use as scratch space - keep that in mind when you purchase. Although yes, you can use your system drive to do editing work (and I have in a pinch), it's not the preferred method for a variety of reasons, not the least of which is amount of thrashing on a scratch drive and when dealing with HD in AIC or ProRES you can easily have 70-90 gigs being used for a single hour of source footage - if you only have a 500 gig hard drive, of which 56 gigs is taken by FCS (as of FCS2, full install with all options, including extra audio voices for SoundTrack) and who knows how much else for other misc. things, you can easily get down to having 350 or less gigs free - that doesn't leave a lot of working room for HD video - especially a project >1 hr.
4) Systems that have replaceable parts fall in a more gray area - for example, if buying a Mac Pro, getting it with a GT120 to save money now may be a fine option as it's EXTREMELY easy to swap the video card with another one later on (simple example, my mac pro came with a ATI 2600, it was inexpensive in that config - I have since upgraded to an aftermarket 8800GT, and plan next year to move to a higher end card still).
Yes, buying a new system is sometimes hard, especially when you are attempting to get the absolute most bang for your buck on a potentially tight budget.
Some things to ask yourself:
* Do I need/want the portability of a laptop?
* How much will I need to spend for extra (external for a laptop or imac or mac mini) storage space to act as a scratch/render drive? (including chassis, cable, hard drive)
* How much screen real-estate do I really need? Can I do what I want in 1440x900 or do I need a screen capable of 1680x1050 (through an external monitor) or 1920x1200 (17" MBP, external screen or iMac)
* How much am I willing to pay for RAM upgrades? You're going to want at least 4 Gig. I've edited with 2, 4 or more is better.
* Can you sacrifice the features of color you'd theoretically loose w/ 256m video?
* How much physical space do you have to put this machine? Will a 24" iMac fit? Will only a laptop fit? Will a machine with speakers, dedicated tower like a Mac Pro and a separate screen fit?
This machine is a major investment, and, as you can see (and I'm sure already knew) - not something to be taken lightly. A lot of serious consideration must go into your final decision. If you have an Apple store, and an Apple reseller near by, I strongly urge you to go into that store and look at the various systems (including refurbished or trade in Macs that may have a warranty option still (refurbished Macs first suggested by D3v1L80Y - which is a good option - in all honesty, 3 of my 4 Macs are used systems as I couldn't afford to get new) ) - talking about what something looks like and feels like is a far cry from actually going in to try it out. Many stores may even have systems setup with Final Cut installed so you can get a feel for what you like and what works for you. You can also see about making an appointment at a local Apple store (assuming there is an official apple store there) to go in and talk to them to help match you with the best machine within your budget.