I am doing a 1800 calorie a day and I wanted to know what would be a good amount of protein . 3, 4 or more. And Do you weigh before or after cooking???

I think a daily protein gram total of around 70 - 75 is ballpark for 1800 calories, generally. People on a low carb diet eat much more, and those on a low fat diet eat much less. You should check with your doctor or nutritionist, for an accurate assessment.

I weigh/measure meat, beans, lentils etc. after cooking.

When you see data about protein like meat, chicken, fish it is almost always the uncooked weight since the cooked weight can fluctuate quite a bit depending on cooking method.

You should realize that the weight of meat does not directly translate to grams of protein. For example, beans have lots of carbohydrates in them, so their mass is made up of protein and carbohydrates. Same with meat. So, look up how much protein (usually in grams) per ounce of meat before you figure out grams of protein. I use uncooked weight, since I like to add vegetables and sauce and stuff when I cook meat. I shoot for 0.5 to 0.8 grams of protein/pound of body weight. (I have read some exercise sites on the web and that's where I got my number. It works for me. Protein makes me feel full.)

Also, I eat about 1300-1700 calories per day, and much of my protein is dairy and vegetable based.

Here are websites I have found useful:

www.stumptuous.com
www.nutritiondata.com