I treat it like spaghetti! You can cook it a couple of ways. If I have time, I just stick the whole darn thing in a dish and bake it at 350 until I can poke a fork in easily. If I don't have time, I cut it in half, scoop out the seeds, place cut-side down in a dish with 1/4 cup water, cover (I use a corning ware dish with a lid), then zap in the microwave for about 8-10 minutes, until soft. Let it cool a little bit, then take a fork and pull it down the sides of the squash into strands.
Once you've got the strands, I've done a number of things. I've put some lite margarine and parmesan and baked it, I've used marinara or meat spaghetti sauce, I've sauteed it with other veggies. My 5-year-old will even eat it!
There was a great recipe for spaghetti squash in Cooking Light last month (in fact, a search there turned up dozens of recipes...check out www.cookinglight.com ). You layered the squash strands (cooked) in the bottom of little dishes (this would be for a side dish, but I wanted it as a main dish, so I put it in two small casseroles), top with sauce (recipe has a homemade recipe, but you can use a jar; I put meat in mine to make it more of a main dish) then top with a mixture of:
1/2 cup (2 ounces) grated fresh Parmesan cheese
2 teaspoons chopped fresh oregano
1 teaspoon chopped fresh thyme
1 (15-ounce) carton fat-free ricotta cheese
Bake at 400 degrees until the top is browned...about 50 mins (that's how long my big ones took, and how long the recipe called for with the little dishes. Long time, but well worth it...this is fantastic! )
There's a recipe in the SBD Book, but basically, it's like the other chicks said - You just cook it, then treat it like pasta!
I topped mine with Tomatoes, red onion, garlic, zucchini, whatever! Nummy, Nummy!
Beachgals post has some great ideas. I tried spaghetti squash once and hated it...and there's very few foods I actually hate. the baked with parmesan sounds good. Maybe I'll get adventurous this weekend.
You /can/ use it just like pasta in casseroles and such, but it is very watery, so you will need to reduce the liquid or you'll end up with a soggy mess. The flavor and texture will not be the same, but that doesn't mean they'll be bad. Personally, I find the wateriness of spaghetti squash too off-putting - I haven't made it in years.
hMMM... I have always wanted to try the spagetti sqaush idea. I just dont know about it though. I am not a big veggie eater. If you had to compare it to something what does it most taste like?
a hint that I learned, look for the smaller ones if you are going to cut it in half. If you get the bigger ones, sometimes the knife gets stuck. I have this fear that I'll cut a finger off wrestling trying to get the knife out.
Ok, so I bought a Spaghetti Squash
Long time, but well worth it...this is fantastic! 
)
