Weights

Will working with weights take away any of my endurance? And when I gain more muscle mass will it make me slower because of the weight or will I still have a faster speed sense I run so much?

Im just asking all these type of questions because im...

getting ready to run on a cross country scholarship and am working with different approaches and see which one produces faster times.

That's a really good question. When you use weights try to use lighter weights and do more repetitions. This will make all the small muscles really strong and will work your fast twitch muscles. This will build up your endurance. Using extremely heavy weights and only doing a few repetitions will build muscle mass (bulk) and since this is working your slow-twitch muscles, you could slow down a bit. Body builders do this.
You definatley need lots of toned muscle because that will increase endurance and time.
Peace