After reading the decision (PDF), it's actually clear that this isn't a victory.
Yes, the court affirms the proper reading of state law, but get this -- it claims it can't compel the governor to follow it. It vacates the lower court's order that the special senate election be moved up to the top of the ticket, and literally hopes that Barbour does the right thing. But there's nothing in that decision that forces Barbour to comply with state law.
"This Court, and other courts, have long recognized that the Governor must be allowed to perform his duties without interference from the courts."
"That is not to say, however, that the acts of the Governor and Secretary of State are beyond review of the courts. Once an act is performed, it is then subject to judicial review and, if the act is found to have violated the law, the constitutional officer is subject to the penalties provided by law."
Apparently, in Mississippi, the governor is a dictator. And if he ignores the law? Well, then he might be subject to the penalties provided by the law. Of course, this being an election statute (full code is here (PDF), there are no penalties for ignoring the proscribed ballot placement. The drafters of this statute assumed, stupidly apparently (since they live in the Banana Republic of Mississippi), that the government would actually adhere to the letter of the law.
Update: No thanks to the Mississippi Supreme Court, Haley Barbour has decided, out of the goodness of his heart, to actually comply with state law.
A spokesman for Gov. Haley Barbour says he will move the special election for Trent Lott's old Senate seat off the bottom of the ballot [...]
A majority of justices ruled that a 2000 state law requires all federal races to be near the top of the ballot. But the majority stopped short of ordering Barbour to elevate the Wicker-Musgrove race.
Barbour issued a brief statement: "The Supreme Court has spoken; so be it."
His spokesman, Pete Smith, elaborated by saying "the governor is going to comply with the ruling and the Senate race will go near the top."