Since US Airways is a Star Alliance carrier, you can use your US Airways miles to book awards on Continental/United or any other Star Alliance carrier.

I don't believe you can transfer miles from US Airways to Continental, unless you want to use points.com and lose a huge percentage of the value (which I would never recommend). You can still credit miles earned on United/Continental to US Airways if you choose. Or you can start accumulating miles and status on United/Continental.