I have replaced the saddle and the pedals on my LeMond (nevada city) and now want to replace the stem but dont know which one to buy?
The one on my bike is one piece, it runs from my handlebar then does a right angle and go's into the fork, if I buy a new stem, where do I get the "down tube"

Also, how do I know if it should be threaded or threadless :confused: , and do I just measure the length of my old one and get the same size (even though I do feel like I'm streaching with the one I have now)

Sorry about all the questions

Sounds like you have a threaded headset, therefore you need a quilled stem.....the traditional kind.....all one piece elbowed. It's best to just look for another shorter quill stem, if you're looking to replace it with a shorter one......sounds like the one you have now is a bit too long for you.
Forget about converting to an Ahead-stem (current style stems)......you will end up spending alot more.

Another options is to get a quill to threadless stem adapter. THen you will have alot more options of stems open to you.
Tri-zone carries them for $10. Then if you decide to go threadless in the future you already have the stem.
They also carry some threaded stems.. Also titec has a closeout on their ti threaded and threadless stems for around $50