Brand new army!

After selling off my fantasy armies, I've acqired a brand new one and I'm really excited about this new venture. I went and bought 2 Dark elf battalions, a sorceress and the army book. I'm starring at 40 corsairs, 32 Dark Elves with Repeater Crossbows, 24 Dark Elves with Spears, 10 Cold One Knights, a sorceress. . . And not a clue how to organize them into a managable force. I like the idea of bolts flying everywhere, but they don't pierce armor very well. There, in lies, the dilema...

So, how do I get this force to be a formidable opponent?

That force? You can't.

Use the Corsairs for bits, they suck. Buy 2 Hydras. Buy a whole bunch of Cold One Knights or BlackGuard depending on if you want infantry or cavalry heavy.

Then read my[URL="http://nike40k.blogspot.com/"] blog[/URL] where I focus quite a bit on Fantasy in general and Dark Elves in specific.

I disagree.
Corsairs are good with a repeater handbow, they aren't the best unit for value out there, but they can do allot of damage to large, light, units by moving up, shooting, and then letting them charge you and shoot again. I'd take them in 2 units of 20 as any less and they wont stand up in combat any more and unless you do them in horde, which can work, your wasting to many shots, it also gives you more units and thus a larger battle line and some more flexibility.
Hydras are very powerful so long as they don't get killed by a cannon, but if you want to play for fun people wont appreciate two hydras at 1500, however they are very effective and using one can give you some very good infantry munching power as they can often kill 10-15 light infantry on the charge, and they can also be used against heavy units that you don't want your corsairs to be in combat with, however as i said two isn't very sporting in a fun game but can be very good in a competitive army so long as they are protected.
Units of 10-20 crossbowmen work well, they don't pierce armor very well but they can pump out enough shots that mathhammer will smite heavily armored foes anyway and I've often found that softening up a heavy unit with a few rounds of shooting and then charging cold ones in works well.
Spearmen are good and always useful just to tackle other large units, they can work well with cold one knights if you can hit a unit in the front with spearmen and on the side with knights and the same tactic can be used with hydras. They can also work well as a tarpit unit against heavy infantry to protect your corsairs as they get rid of light infantry.
Sorceress' are always good and its worth having at least some magic in a dark elf army, i find deploying them with crossbowmen works as it gives them the protection they need and many of their spells are 24 inch range anyway, having a master or dreadlord is useful as well so id consider taking 2 characters as the master/dreadlord helps to add some punch to either cold ones or infantry.
If you wanted to get more models id recommend reaper bolt throwers as it let you hit at long range and in a ranged army that can often be vital.
Don't forget you can always test units out in 750 point battles with a mate and see what you like and what you don't as well as what is effective against certain units.
I'm no expert at warhammer but having played dark elves with combos of all these units this should be fairly sound advice.

Thanks for all the help so far. I've been able to play a couple games so far and the massive amount of shots is astounding. Played a smaller game with goblins and just shredded them and a friend had some other Dar Elf models he let me use against skaven. Dark Riders and shades are incredible, and the sheer volume of shots is what helped the most. Tried the Corsairs shooting/stand and shoot tactic and that really does a number on horde type armies.

Question though, could you give them a Banner of Murder and give them AP rule for shooting and Melee'?

One the topic of the banner I'd think giving them the Razor standard, armour piercing for -2 to AS from shots, or the Eternal Flame, for flaming shots, would be pretty good options, allows for the unit to deal with either heavily armoured units (low toughness as well is great) or tough regenerating/flammable monsters (hydras/trolls/HPAs/Treekin/Treemen). I don't play or play against Dark Elves to offer much more advice than that.