Well, belching is usually only a good thing in Eastern societies. But in Western ones (where the utensils are fork, knife and spoon) it's a safe bet that a nice big burp at the end of dinner would not be appreciated. But if you're ever in China, please feel free to give your best belch, making yourself rival to Booger on Revenge of the Nerds. <img src="/images/graemlins/laugh.gif" alt="" />
And, you are expected to get up each time you have to blow your nose. The reason being the germ factor, e.g., don't blow your germs on my food. Also, when you blow your nose you run the risk of getting the germs on your hands, then on mine when I have to ask you to pass something. So if you blew your nose at the table then you'd still need to get up to wash your hands in the bathroom, so why not just do it all together.
If your nose is running, then I think it'd be best if you opt not to dine that day or take a really good decongestant so you don't have to get up as often. But you can always explain to your dinner guest that you're sick and see if they don't have a problem with it. But still I recommend just getting up. <img src="/images/graemlins/wink.gif" alt="" />