HD 4870 or HD 4870X2?

I don't think that you should be crossfiring such an old card like the HD 4870.Get a more powerful single card.

If you run games in window mode,then both cards options are a waste because you can't use SLI/CF don't support windowed mode.

I would recommend something like a 68xx or 69xx series for current gaming from AMD's selection. From Nvidia's selection, the gtx 460, 470, and 480 are all very good, unless you want a 500 series.

I have 2 x 4870s in crossfire on the Asrock 880G Extreme 3 and it works great, I can play all the games I have on highest settings at 1920 x 1080 as long as you don't pay to much for the second 4870 then its a great setup. 8x is fine for the 4870 i think you only lose 1-2% fps on older cards when running in 8x slots compared to 16X.

The hd5870 loses only about 1-2% of its power in a 8x slot. Anything under a hd5870 loses nothing in a 8x slot. My hd6850 works fine in a 8x.

Ive been searching around on google and some are saying crossfire does some are saying it doesn't support windowed mode and someone even saying saying it will work with windowed mode for directx 10 and 11 games but not 9. Now my only quesion is which would be better for me to have more power for multitasking. Should I try and get crossfire or get a newer single card with 1 or 2GB of vid ram? I mostly play second life and wow and also gta 4 and sims 3 and I preferably like to have everything in windowed mode but if crossfire for sure doesn't work with windowed mode I should just get a newer card?

Get a hd6850 or hd6870. The hd6850 can OC well, even too the power of a hd6870. If you want more than that, a hd6950 would do. For Nvidia the gtx560 when it comes out or a GTX570.