Will the nikon nikkor 35mm f1.8 be equivalent to about a 50mm on a d90?

I have heard people say that the 50mm f1.8 is equivalent to about a 75mm so dose that mean the 35 will be equivalent to about a 50mm
what would be better for party photos and portraits.

Close. The crop factor is 1.5x. So if you do the math, it would be equivalent to 52.5mm.

You can use either a 50mm or 35mm for portraits. It's just a matter of the distance you want between you and your subjects. The 50mm is longer and the 35mm is wider, for better full body portraits. Setting the obvious aside, I'll leave it up to you to decide which one you'll pick because you know your own shooting style best.

While using a 35mm lens on a crop factor camera such as a D90 will increase it's apparent focal length to 52mm, the lens will retain the characteristics of the 35mm lens, namely perspective distortion.

All wide angle lenses have some degree of perspective distortion, and this is not necessarily a bad thing, except for portraiture. You will never see a professional use a wide angle for portraits as perspective distortion results in big looking noses and rounded faces.

Here is a webpage that shows what perspective distortion is when compared to a 35mm and 50mm lens shot with a D90:

http://www.althephoto.com/lenses/35mmprime.php