Sorry for confusing title - not quite sure what to call this. I've been reading old posts but am still confused as to what to do:

I want to edit video (at the moment HDV, possibly in the future HD) and put it onto dvds for festival submissions, and need a mac to do it on. Im deciding between a Mac Pro (but I suspect its capabilities are more than I really need) and an imac.

Ive seen a second hand imac 20 inch 2.4GHz Intel core 2 duo, 250GB, 1GB (would add more) RAM NVIDIA Geforce 8800 GS 512MB VRAM for 550

or I could get a:

20 inch imac 2.66GHz Intel core 2 duo, with 640GB, 4GB RAM, NVIDIA GeForce 9400M graphics processor with 256MB of DDR3 SDRAM shared with main memory for 950 with educational discount

From previous posts I get the impression that this is fine for Final Cut Express but not Final Cut Pro. Am I right? If so my question is - is there much difference between express and Pro/Studio? My editing will be quite basic with not many effects (its documentary) - will I miss not having the Final Cut Studio? Can express handle HDV and HD? and will I be able to export it to DVD for cinema viewing with Express? If Express or Pro can only do HDV, that may be fine as I may upgrade when i get to HD, but it would be good to know.

I don't mind it being slow, but dropped frames and stuttering playback will drive me mad.

If these models are not enough I could get the 24 inch imac 2.93GHz intel core 2 duo, 640GB, 4GB RAM and one of the following:
* NVIDIA GeForce GT 120 graphics processor with 256MB of GDDR3 memory
* NVIDIA GeForce GT 130 graphics processor with 512MB of GDDR3 memory
* ATI logo ATI Radeon HD 4850 graphics processor with 512MB of GDDR3 memory

Will this be sufficient? And if so, which graphics card?

If not, I might as well go Mac Pro, which I know would be the best option , but I feel it might be more than I need. Is It? Its 1400 more than the cheapest imac when you add on a cheap monitor etc.

Thanks for reading. Any ideas/thoughts?