The source for the data are tables provided by wikipedia
Murder Rate: http://en.wikipedia.org/wiki/List_of_countries_by_intentional_homicide_rate
Gun Ownership: http://en.wikipedia.org/wiki/Number_of_guns_per_capita_by_country
First we look at all the countries. The correlation coefficient between gun ownership per person and murder rate per person is -0.19963579. A negative coefficient implies that as gun ownership increases, murder rate decreases. However, the correlation coefficient is to low to imply any correlation at all, so we conclude there is no correlation between how many guns is owned in a geographical area and the murder rate in that area.
Another way to look at it
Ok, but there is a lot of very violent 3rd world countries out there we should concentrate only on the civilized countries. That is fair, lets then look at countries whose murder rate is 5 or lower. The correlation coefficient is -0.108910882, to low to imply any correlation.
Finally lets single out only the western European countries. The correlation coefficient becomes a positive .472156671. Statistically this is a weak or moderate correlation. Which would imply that more guns equals higher murder rates. However in this data set United States is a very large outlier. If United States is removed the correlation coefficient for western countries goes to -.16, again signifying that there is no connection between amount of guns owned, and murder rates in any geographical location.