Okay, bows vs. hornbows vs. greatbows vs. crossbows vs. maile vs. plate vs. lorica.
Bows
Bows sucked. They were, at best, for hunting or for killing poorly armored enemies. On the other hand, you could ride a horse and use one, and if you were good enough you could get an arrow through a weak point if you were close enough (or if the target wasn't moving).
Hornbows
Hornbows were much better. Long range, and the material allowed for more flex, which meant more acceleration time, which meant the arrows travelled farther and hit harder (and had a longer "penetrates shield or metal range"). And you could wield them on horseback. Unfortunately, these composite bows relied on glue to hold them together, and tended to fall apart in any kind of humidity. This limited them to desert and steppe dwellers, generally nomadic barbarians. (And was one reason the bastards were so feared.)
Greatbows
Greatbows had all the range and penetrating power of hornbows - maybe even a little more - and since they were non-composite, they didn't fall apart in humidity. Of course, you had to make sure to keep either yew or hickory on hand. And they were so big that you had to be at least 6 feet tall to use them. You also needed great big arm muscles to use them. (DnD elves? Too short, too skinny.)
The nice thing about your greatbowmen is that if you have command over the terrain - such as easily-placed stakes to deter charging cavalry - you can shred almost any attacking force. The English matched 1500 greatbowmen vs. 45,000 French heavy cavalry and very nearly won. (Granted, they were just French, but France was rich back then and could afford the best toys. So it's still like almost winning against 20-1 odds. Maybe 15-1. Well, okay, but no less than 10-1.)
(England trained all the greatbowmen they could, but they only had 1,500 available. That says something about the requirements.)
To train up greatbowmen takes either a few months of dedicated training or 5+ years of weekend drilling. At least one king made it a requirement that anyone who was physically qualified _had_ to drill on the weekends.
Yew eventually became in critically short supply, by the way, and hickory was only available in America.
The Japanese had a greatbow variant that samurai could use on horseback, but I don't know the specifics.
Note that compound bows, the ones with pulleys, allow someone with a given strength to use a stronger draw, leading to even more range and penetration. And greatbow skill transfers to compound bows without any major retraining required.
Assuming seasoned wood is available, an experienced bowyer can make a greatbow in about an hour.
Crossbows
Crossbows win against bows, having better range and penetration, but fail against hornbows and greatbows, having less range and penetration and _much_ less rate of fire.
On the other hand, they are literally point-and-click weapons, and recruits could be trained up for volley fire in less than a month. No need for 6+ foot supermen, either.
At one point the Pope issued an auto-excommunication if you used crossbows against your fellow Christians.
Beryllium bronze would make crossbows that negate most of the disadvantages in comparison to greatbows. However, beryllium bronze is an advanced material - dwarves can have it as a secret technique, but humans shouldn't be able to discover it with medieval technology.
Crossbows are inevitably expensive, because of the multiple parts required. And they take a while to put together.
Maile
French for "mesh". (Remember, in the Middle Ages the French convinced everyone that they were cool. It was a f**ked up time.) DnD's "chainmail" is taken from a Victorian-era bit of pseudohistoric romantisation of maile. But, yeah, interlocking rings of metal, all the weight on the shoulders, stops slashes and most chops but can't do much against trusts or impact weapons. "Pile" arrows, with narrow points, go right through maile with any luck, and is in fact what they were made for. (Although the broadhead design leaves nastier wounds - those barbs, etc.)
Once you have the 'wire' stuff that makes up the individual rings, maile can be assembled by an apprentice under supervision.
Plate
At first just plate over the more rigid parts of the body (with maile underneath), the state-of-the-art eventually including fluting. Joint protection was available. Weight was slightly higher than maile, but was distributed far better. A properly made suit allowed for somersaults and flips, and such armor commonly bore the proof that a handgunne bullet had been discharged into it without penetrating.
Expensive as hell. You needed high-quality iron and a master armorsmith. It was not unknown for ambitious rulers to promise knighthood to the sons of wealthy merchants if they would provide the armor themselves.
(Another dwarven secret can probably come up with bessemer steel, if not quite with the same process because that would make bessemer steel way too cheap. If you have an elemental that can separate out pure oxygen, you can make high-quality steel from any quality of iron, by the way.)
Properly armored knights tended to _not_ die in battle, by the way. You needed to be within 50 yards with a greatbow to get through the stuff, or you needed to mob the knight with enough people to hold him down and fend off any rescuers for long enough to pry the armor open and get a knife through.
Lorica
What the roman legions had. The inspiration for DnD "Banded Mail". If you could afford the metal version, it was very nearly as good as plate, but required much less expertise to put together. (Among other things, it doesn't have to be fitted to the person at the time of forging beyond general size requirements.)
Working man's armor. The only real disadvantage to plate is that it doesn't have the joint protection, so expert-level archers can do the joint targetting thing, and someone who can get in with a knife might be able to slip between the bands of metal. (This can be fixed with maile, if you don't mind adding ~10 pounds to your load.)
-Albert
[ July 03, 2007: Message edited by: Albert the Absentminded ]