I would say, __no__, but let me elaborate on why and see if there's a possible way around the issues:

Assuming you still have environmental dangers, accidents and people wanting/having to kill each other:

- Projectile weapons of other sorts have technology that you can use for other purposes.

    - For example, the idea of a crossbow is pretty much a bow with the string pre-drawn. The application isn't that simple, but as long as you have strings and understand the idea of switches and materials, if you need weapons, why not make one?
    - Muskets use the same principle but with explosives instead of a string - again, you will discover explosives by accident and need to understand them. Finding out that they're very effective when placed in confined spaces and tubes is a short step.

- If you figure out how to control explosions and place them in tubes (cannons, mortars, rockets) and you need weapons, you're going to use them that way because, if you don't, your enemies will.

- Weapons and weapon-like tools aren't just for killing people; they're for hunting as well. More importantly, they're used to protect yourself from animals. If this isn't easier, exploration is harder, so is guarding flocks of animals and crops.

    - Also, there's a lot of tools that can be used as weapons: ice-picks, axes, climbing hooks, boot-spikes, dynamite, nets, fences, rope etc. If you _can_ think of weapons, you've already thought of using these as weapons.

So, the way I see it, as long as weapons for either attack or defense can occur to you, every technology is a potential weapon. There will be strong environmental pressure to develop better ones and most of them are relatively simple applications of engineering principles.

However, you _might_ be able to have a civilization with starships but _no_ advanced weaponry [iff][1]:

- There is an incredibly powerful cultural drive towards pacifism after rudimentary weapons are developed.
    - This assumes that _for some reason_, _everyone in the world_, the bad, the good and the ugly, decide to be pacifistic. Either there is no warfare or inter-special dangers, or it is conducted through other, more effective (for that species) means.

- Said species encounters _no_ other species that doesn't share its own perspective. If they met a regular species, they'd be forced to develop weaponry or be enslaved or wiped out. So such a species would either have:

    1. met no one else and is ultra pacifistic
    2. met only ultra pacifist species and civilizations
    3. has come up with means of attack and defense that are far superior
    4. met a non-ultra-pacifistic species and has been wiped out or enslaved already

I don't see any way around these limitations.


  [1]: http://en.wikipedia.org/wiki/If_and_only_if