Mountain Biking - Winter pants?

This might seem like a dumb question .......but what do you guys wear for your legs in the colder weather on the trails???? Do you wear tights (like roadies) cargo pants, jeans or anything else??
I haven't ridden in the cold yet, and was considering wearing some khaki type pants I have that have zippers on them that converts them to shorts. Give me some practical advise about what you use....thanks.:)

I have found the best thing to wear is a cheapo pair of cotton sweats. Make sure they aren't baggy, but they are warm, comfortable, and if you crash and tear them up they make great shorts when summer rolls around, plus you aren't out $100+ on a pair of technical bike wear.

Nylon wind pants over cycling shorts over polypropylene thermal long johns. Good down to about 10 to 15 Deg. F.

Above 30 deg. F I lose the long johns.

Leg wrap on the drive side

I wear Pearl Izumi long tights that are fleece lined and then i wear cargo shorts over those. My legs have never been cold

Cargo shorts over long johns or "thermal underwear" is great for out cold times. Although in Texas the cold season is really short, so the shorts are warm enough most of the year. The thermals are cheap and easy to find/replace.

I've biked into minus 30 plus with a wind chill. You can't chance getting damp in cotton or you're into hypothermia in no time.
I find polyester is the life saver. You can get it in wicking underwear as well as fleece.
On the bottom I wear my chamois and a polyester underwear. I top it off with a waterproof.

Up top I start with wicking underwear, layers of polyester with a fleece top with a very high neckline. I top it off with a waterprooof/windproof with pit zips and Scotchlite strips.

For the hands I wear polyester glove liners and then gloves.

On the feet I wear two pairs of wicking socks and leather half boots.

I put a shower cap on my helmet, and a tube that fits up to by eyes as well as earcovers. I've tried wearing goggles but they either steam up or freeze and bother the skin around my eyes. Right now I blink alot to keep my eyeballs from freezing.

Be careful not to work up a sweat. Slow and steady does it. I carry a change of clothes in my pannier just in case.

Allan

Nylon warm up pants over sweat pants. You may want to wear bike shorts under the sweat pants for the padding. I always wear boxer/briefs to prevent chaffing which bike shorts help to prevent too. I need to start wrapping my right leg in tape to prevent the pants from getting sucked into the chain ring.

I find nylon windpants the best on the outside. Underneath that the choice is yours and depends greatly on the temperature. I don't find that I sweat enough on the bottom in the cold to cause problems with moisture inside the pants. The top is a different matter. I find I've got to use breathable/wicking materials or I get wet and cold from sweat.

I wouldn't recommend the zip-off convertible type outdoor pants. While the material in these pants generally wicks, you need more protection from wind and personally, I find the feel and movement of the zipper around the knee to be a royal pain when biking.