excellrec,
Volts don't really figure into the equation, as far as when the fuse blows, since the fuse element is of a low enough resistance that negligible voltage is dropped across it. Rather, it's the current that's important. Since power dissipated in the fuse element is what causes it to blow open:
P = Vsq/R or Isq * R
HOWEVER, the voltage rating of a fuse is still very important for other reasons. The voltage rating refers to the maximum open-circuit voltage permissible, so it's perfectly OK (and quite common, in fact) to use a 250V-rated fuse in a 120V circuit. If a fuse having a lower voltage rating than the circuit voltage is used, in the event of overcurrent, it may "flash over" and fail to protect the circuit, explode, etc.
Good reading about fuse ratings and terminology:
http://www.connectingindustry.com/news_story.asp?story_id=13649