Deadlifts?

Ok, Hey guys, I just started working out on my legs, and since I only have a dumbbell, I'll have to do deadlifts, I just have a few questions though, and thanks to anyone who has the time to answer them.
1. Just how effective are deadlifts?
2. How long before I see results?
3. How many should I do a day?
4. I just did about 20, and my legs hurt, is this because I'm not used to leg exercise?

1. Just how effective are deadlifts?
 
Very effective for gaining size and strength.  At least equal to squats, if not superior, imo.
 
2. How long before I see results?
 
Depends on how much weight you use, your goals, etc. 

3. How many should I do a day?
 
Deads are usually done for size and strength, and fairly low volume.  They are not a high rep exercise.  At higher weights you fry your back.  My routine is usually something like 185x10-12, 225x8-10, 275x6-8, 325x4-5. 

4. I just did about 20, and my legs hurt, is this because I'm not used to leg exercise?
 
Um... it's more likely the high volume that did you in.  I did 20 rep deads (barbell ) once, and am barely here to tell about it.  They're worse than 20 rep squats.

I do deadlifts once a week.  I work at 300x10, 315x8,325x4-6.
 
You probably wouldnt want to do the exact weights, but I would recommend something like 60% of your max for 10 reps, 75% fo your max for 8 reps, 85% of your max for the final set.
 
Its a good strength and size builder.
Make sure you have an experienced person check your form.  One trick is to first make sure the bar is close to your body, second, make sure your heels are firmly planted, third, look at the ceiling the entire time (to get your neck positioned correctly) and finally, the bar should ride up your leg a bit, its normal.  Thats why you see powerlifters with powder on their legs.
At the top, drop down, so that the weight is just controlled enough to not be lost, but your back isnt rounded.  The descent is not as important as the ascent.
 
I had no visible muscle on my back and traps.  In 3 weeks, I had a lot.  This might not be the same for you, but I love deadlifts!

Squat 385, Bench 235, Deadlift 450 @ 181.