[gov2001-l] standard errors of interaction terms

When you run a linear regression that includes interaction terms, how do you interpret the standard errors? For instance, we have two dummy variables, one that indicates the presence of a popular initiative on a ballot and another that indicates whether a presidential race was held that year. So we get estimated coefficients and standard errors for: initiative presrace initiative*presrace When initiative and presrace both = 1 (both present on the ballot), the total predicted effect of the presence of an initiative equals the coefficient on initiative plus the coefficient on initiative*presrace. What is the standard error for this predicted effect? Do we add together the standard errors for initiative + initiative*presrace, or do something else? Thanks! Anna