Hi,
to try to answer your questions:
1) Will it work with no errors? It should as long as you're getting a Macbook that has a 9400m or better graphics chipset. FCS3 has higher requirements for video memory for the Color application, but not everyone will require that aspect - plus you're referring to FCS2 so
2) Will you have long render times with 1080i? Depends on what you're doing. If you have to export - be prepared for it to take time - especially if you're transcoding from say 1080i to 720p via sequence settings.
3) Depends on the amount of simultaneous streams and which effects / transitions you have chosen to use in your video. If you stick to realtime capable ones and not too many simultaneous video streams you should be ok.
Now - as a note - I would strongly urge you to spend a few extra $100 to get the 13" MBP - the reason: FW800. The current Macbook has no firewire. To edit video, you really need to use a disk other then your boot/OS drive for scratch / render / scrub / etc. work. With the current Macbook, you'd be limited to using USB. Although you *can* edit using an external USB drive and HD video (I have in the past) - it's not near as pleasurable, and you can have fewer streams prior to rendering requirement, and with the speed, you tend to have some of your effects go from real time to render required.
I have edited on a late '08 Aluminum Macbook (2.4 GHz, 2Gig ram) w/ an external USB drive. I did it only when I had to (at work) until they got me an iMac to use. Whenever I went home, I used firewire (or one of my other internal drives as I have a Mac Pro at home) as my scratch media.
Overall, I think you'll have a much more pleasant experience on the Intel Mac editing HD footage; but as I mentioned, I strongly suggest you get the Macbook Pro 13". It's not much more expensive and it has Firewire.