How To Serve Vintage Port
The port should be at the correct temperature prior to decanting. One thing to watch out for is that the bottle or decanter shouldn't be left on a hearth (especially at Christmas), near a radiator or in bright sunlight as it will warm up just a little too much and the fine balance of the wine may be spoilt. Older ports should be decanted just prior to serving and a constant temperature after leaving the cellar is preferable.
How Long Will It Keep For?
It depends on how fast you drink it! Younger wines may last for a couple of days, older wines even less. We tend to open Vintage Ports at family gatherings and drink them after lunch or dinner; the bottles tend to be finished at the meal. However, if you do need to keep it overnight, a vacuum style stopper will help.
To appreciate the port at its best, a glass that can be "swirled" is best. A tulip shaped glass allows this and allows a decent sniff (or nose) from the wine. I've taken to drinking Vintage Port from a whisky tasting glass which has a very pronounced curve in at the top giving a really intense nose.
There's a lot of tradition (or some might say twaddle) about how port should be passed (to the left without ever resting on the table etc etc). It should be passed to whoever would like some next, and ideally be poured for them. Anything else is simply delaying the moment. Controversial I know.