background change help

I've been having a hard time getting this background sawp to look natural. The picture I've linked to is as good as I've been able to get it, but something still doesn't look right. Could anyone check it out and help point out what I need to do still?

Thanks
This is the picture

looks good to me, maybe add shadows?

lol, that's exactly what i did, but for some reason it still didn't look right, maybe im just not adding the shadow correctly... Here's a link to the one with the shadow .

Hm...it looks alright to me, but something still doesn't look right :p .
To me it doesn't seem like you can really do much more to it if you want the background to look natural, beyond getting a new background. I think the problem just lies in the backgrond you have, it doesn't have a 'natural' or 'real' look to it in the first place so it doesn't precisely fit in with the group of people. The bg by itself just doesn't seem to be a setting to take a picture in...so I guess maybe making your current one seem more realistic (giving it depth somehow, I don't know how you would, but seems like something you might have to do...) is your best bet, either that or getting a new bg.

yeah, depth is definitely one of the things that are bothering me.

The trouble looks to me is that the background is rather 'old' or rather it has a lot more noise than than the people in the foreground. I would be tempted to replace the background with a digitally taked background or at least introduce noise to the people in the background.

I see something weird in the bottom part actually. like the jeans of the girl (the girl with the nea bent) dosent seem to blend with the background,

Spilt,

I like the bottom lines of Bruce Lee you put there. Fantastic!!