Wine barrels can, in fact, be re-used - but the wood "becomes neutral" with regard to imparting desirable effects on the wine itself after 3-5 vintages, depending on the type of wine and the characteristics of the wood.
For those interested, check out the wikipedia page on Oak and its importance in winemaking
http://en.wikipedia.org/wiki/Oak_(wine)
As for cooking with wine barrel chunks/staves, I've found them at a number of places, from online wood distributors to the local World Market. I've used it to smoke beef, venison, and even a spiced pork tenderloin, and I've added it to the grill to add a nice smoke flavor to grilled salmon and NY strip steaks. The wine soaked in to the wood mparts a little bit of a fruity/"winey" flavor, but the predominant flavor is still that of white oak.
Happy cooking!