Can you put enchantments made for weapon on ammunition or is it strictly ammunition enchantments? Ex. The Fiercebane enchantment (MIC p.35) calls out for a weapon slot to be enchanted and says "A fiercebane weapon excels at attacking"
For the purposes of applying magic weapon special abilities, ammunition is generally considered a weapon
That is, for the purposes of magic weapon special abilities, weapons includes ammunition. Were this not the case and ammunition must be specifically mentioned by a weapon special ability for that weapon special ability to apply to ammunition, the only Dungeon Master's Guide magic weapon special ability that can be applied to ammunition is brilliant energy (DMG 224) (+4 bonus; 0 lbs.). Further, the Magic Item Compendium gives each magic weapon special ability a Property entry describing onto what the magic weapon special ability can be placed, and no Property entry specifies ammunition. (A strict DM could, instead, read this near silence as limiting ammunition to only enhancement bonuses and the weapon special ability brilliant energy, but I'm not sure why a DM would, especially since such specialty ammunition can be randomly generated using the DMG's own tables and Wizards of the Coast's own published creatures employ specialty ammunition.)
Note that some specific magic weapon special abilities can't—for a variety of reasons—be placed on some or all kinds of ammunition and that some—but far from all—specific magic weapon special abilities are passed on to the ammunition by the magical projectile weapon from which the ammunition's launched.
Finally, note that the weapon special ability fiercebane (Magic Item Compendium 35) (+1 bonus; 0 lbs.) has the notation synergy (explained on MIC 224–5), so fiercebane ammunition must first have the weapon special ability bane (DMG 224) (+1 bonus; 0 lbs.): a +1 fiercebane arrow has a +3 enhancement bonus equivalent.