How much does the name of undergraduate school matter?

Generally, advanced degrees, especially MAster's degrees from US schools will never hurt your application unless you have that Master's degree in business administration. Most top schools will not let you "double dip" by getting a "second MBA" when you already have one or the equivalent. As for the unknown school in Uzbekistan, as long as the degree is recognized by accreditation standards as a four year undergrad degree, it should be fine, but it generally helps to graduate from top or at least highly reputable schools, no matter where it was (USA or other countries). The better the school, the better it looks to the adcoms. But I would not let this dampen your enthusiasm for applying to top schools. If you have a great GMAT and a compelling essay package, and can demonstrate leadership and progressively responsible and interesting achievements in a post-college careeer, you will have a decent shot.