My PC svcks too much to play Morrowind and I wanted to know if you could play it on the 360.

Yes, you can.

However, Morrowind is 10 years and 3 months old, unless your computer is older than that, it will most likely run better on your computer with shorter loading times and whatnot.

My PC can probably run it quite well.Can I like walk into a Gamestop,pick up Morrowind,and pop the disc in my 360?Or can I download it from Marketplace with Microsoft Points?

You can't download it from the marketplace, no, you'll need a physical copy for the 360. I say this in every thread about MW on the 360, but it needs saying. My (and others') experience with Morrowind GOTY on 360 was extremely buggy and slow. The game would freeze every 10-20 minutes, and my character constantly fell straight through the ground outside of the world. Plus, the load times are terrible. In my opinion, it's a much better idea to play the game on a PC or the original Xbox.