在Android中创建用户指定的线程数

I'm doing a download application for android. The downloading part is now successfully implemented and its working. What I need is to download the file parallel in segments. To be more clear, if the user specify 8 segments, I want to create 8 Threads and do the downloading. So in what way will I be able to create 8 threads dynamically? Also as I'm doing this for an phone how will I be able to maintain the memory consumption at a minimum level? I have not worked with threads before, so I hope you can help me with this. Thank you for your time! :)I'm doing a download application for android. T