^^^ Hmm, unless I know him pretty well I'm not so sure I'd want him hovering around trying to "help". Cooking is stressful enough without strangers in the kitchen. But you can sit him down at the kitchen table so you can talk while you cook.
A half hour is long enough -- most likely he'll be hungry when he arrives. Provide him with a drink and a plate of hors d'oeuvres to stanch the hunger pangs.
Nothing compicated -- just some thin slices of baguette with hummus, liver paté, (both store-bought), smoked salmon, or good quality ham, thinly sliced with Gruyere cheese.
As for the meal, if he's American, he'll be more impressed by how the food looks than by how it tastes. So make sure every plate is beautifully arranged, and garnish, garnish, garnish! (If he's French, Italian, Chinese, or Japanese, you can't get away with that trick.)
Soup should always have a little something floating on top -- chopped chives, croutons, a dollop of pesto sauce or red pepper purée (again store-bought is fine).
Another trick is to buy a couple of squeeze bottles with narrow tips and fill them with interesting sauces, something fun from Trader Joe's or Whole Foods. Then, before you put the chicken breast or whatever on the plate, squirt the sauces on the plate to make a design like a Jackson Pollock.
Some people garnish plates with flower blossoms, but I've never tried that, so I can't tell you what to do.
The best advice so far is, never cook anything for company, date or otherwise, that you haven't tried out first. Preferably several times.
Ideally, you ought to try out the whole menu, because it's easy to be sideswiped by logistical problems. If every dish on the menu needs last minute attention just before being put on the table, it can be a bit overwhelming.
And a good tip for cooking any time is, have all your ingredients prepared before you even turn on the stove. Don't be chopping onions while the mushrooms are sautéing -- that's a formula for disaster.
