According to Wikipedia:
-85% enriched is considered "weapons grade" and is the minimum purity of the uranium in the US's arsenal.
-20% will create a usable bomb
-3% to 5% is what a light weight nuclear reactor will use. This is most common reactor and what Iran claims it wants to build.
-While the uranium could be placed in a dirty bomb, this would not be the best use. Since dirty bombs simply spread radioactive material, isotopes like Strontium-90 are more effective than Uranium-235
Some useful perspective you won't get from the press...