5870 1gb vs 2gb question

The amount of video memory the card has really only comes into play when dealing with high resolutions. Despite what a lot people think, 1080p really isn't that high of a resolution. The 1gb version should be fine for you.

No...1080p is 1080p. 1920x1080 is the maximum resolution unless they specify otherwise.

Any tv (not monitor) that is greater than 1080p would cost a huge amount and be greater than 40".

To answer your question, only a couple games really use the extra memory, and your're only gonna need more vram if gaming at 2560x1600 or a similar res. Its always nice to get more if you can, but if you want to build the system now, the difference is not worth waiting.

if you're thinking about Tri-firing, I don't know if they are going to be just 2GB(1 GB for each GPU), or 4GB (2 for each) but remember that if you trifire, you are only getting for each gpu what the lowest one has. So if you get the 1GB version now, and then get the 4GB version of the X2 (if they have one) you can only use 1GB for each of the other 2 GPUs

Like everyone else said, if you don't plan on using a 30" monitor, I wouldn't worry about it, 1GB should be enough.