Can anyone tell me what the effects are if you enchant a weapon with the seemingly opposite enchantments of fire and frost? Does it make for an even more powerful effect, or do they cancel each other out making the weapon useless?

To my knowledge, they are to separate enchantments in the same weapon that do not effect one another. I know that with my enchantments, they do both damages in a combined attack. However, damages will different from each enchantment depending on the magic/elemental resistance of the enemy.

My last post has been proven wrong there, hence editing and having an actual interest in this post.

If you can double enchant, is it possible to enchant a bow to soul trap and do fire damage?

Yes you can double enchant as long as you are fully perked in enchanting. As far as I know you can use fire and frost on one weapon and get both effects.

One of the perks in the enchantment constellation is the ability to enchantment multiple enchantments in a single item.

Yes. With the dual effect Enchanting perk, you can enchant any weapon with both Soul Trap and Fire Damage.

There is also one weapon in the game that is enchanted with a unique enchantment called Fiery Soul Trap - this is one enchantment that contains the effects of both Soul Trap and Fire Damage. If you find this weapon and disenchant it, you will learn the Fiery Soul Trap enchantment and can put it on other weapons.

If you know the Fiery Soul Trap enchantment and have the dual effect perk, you can enchant a weapon with Fiery Soul Trap plus another enchantment, thus getting three effects from two enchantments.

and if you make something with fire and frost damage both work independent. 20+20 in damage.

Have you heard of the Mace of Molag Bal? In Markarth, there is the House of Horrors. After you finish everything (Mind you it is one of the easier Deadric quests) you get his weapon. It's my favorite. It has THREE enchantments. Damage Stamina. Damage Magicka, and Soul Trap. So, it's even possible to have more than two.

Only on found items, two is the max you can put on custom-enchanted weapons.

I've not maxed out the enchant perk tree so I haven't been able to experiment with multiple enchantments. I just assumed that they would not include something that the user could not generate himself. It sorta takes away from the whole RP aspect a little.

Oh really? That's cool, I have never really focused on enchanting and magic in Skyrim. But I think I may have a look at enchanting my current bow, unfortunately I play on a PS3. (Thinking of building another gaming computer) So I have not experienced Dawnguard as of yet, although, I hear it gives you the ability to craft arrows? Are you able to enchant them?

With the dual effect perk, you can put two enchantments you've learned on the same item. That's it. You don't get any "special" enchantment effects from having maxed out your skill or taken all the perks. The only enchantments you'll ever know are the ones you learn from disenchanting other things. There are some items that have "unique" enchantments and can be disenchanted, like the weapon with Fiery Soul Trap I mentioned earlier.

I don't know if Bal's Mace can be disenchanted or not, but looking at its stats even if you could do so it looks like you would just learn the three enchantments it has on it, none of which appears to be unique and all of which you can learn from a mutlitude of other less valuable items. Disenchanting it would not give you the ability to put those same three enchantments on another weapon since the limit is two even with 100 skill and all the perks.

Yes you can craft them....no you can't enchant them