Ohhhhh ... I have spent the last few years being somewhat of a nut about reading and trying to analyze all the studies out there. As has been said, there are virtually no studies or polls that aren't done without some kind of bias (and polls are as easily biased as studies, if not more so).
I think an unbiased person who has looked at the effect gun laws in other countries have had and analyzed the all the studies could make the case that a total gun ban (nothing else would have much impact, since a person's ability to kill isn't based on the type or size of weapon) would have some effect on the suicide rate (not that the same number of people wouldn't try to suicide -- just that more will fail without a gun) and possibly the domestic violence murder rate (because domestic violence is the one place where an otherwise normal person might grab a gun and commit a murder). Those are all just educated guesses, but I believe strongly they would hold true.
But if you look at the whole issue ... this is AMERICA, not Europe. And we're not in danger of becoming the "wild west" again; in terms of self defense we've never stopped being the "wild west." If you look for them you can find several cases per day of people using firearms to defend their lives and families in this country. So for the murder rate overall, I don't think it's a stretch to argue that it could actually go up, not down.
In America, no matter who's numbers you look at, guns are used for personal defense many, many times more often than people are murdered with them. Unlike many other countries, we have both a history of violence and a history of people defending themselves and their property. I'm not proud of the former, but I certainly am of the latter.
Taking away guns from Americans will have a different effect than on other countries, where self defense is not such a part of the culture. Because they didn't lose as much as we would. (and even so, the effect was marginal at best and didn't affect long term crime trends, or even murder trends, to go down).
When you hear people lamenting our huge "gun murder" rate and comparing it with countries like the UK, with the claim that only our easy access to guns makes this happen, ask them why our NON-GUN murder rate per capita is twice as high as in other countries? I mean, if guns are the problem, then why aren't ALL murders in this country committed with guns, and why isn't our non-gun murder rate LESS than other countries? Given the facts, no one who looks at the statistics at all can claim that our murder rate would drop to that of other countries if we take away guns, because the numbers just aren't there.
It's because the gun culture isn't the problem in this country, the violence culture is.
And taking away guns isn't going to fix that.
My .02. I am not actually a professional stastician, though I do play one on the internet.