I was having the same 'not in sync' problem although in my case, the message was slightly different:
avrdude: stk500_getsync(): not in sync: resp=0x30 <-- 30 instead of 00.
Also, the TX and RX LEDs were never coming on.
I looked through many forums and tried the suggestions but nothing worked.
I then played with the COM port and it fixed the problem!
I was using COM3 which was the default. As far as I knew, I did not have anything using COM3 but then I remembered playing with a USB to Serial card about a year ago. So for the heck of it, I changed COM3 to COM9 and it worked! YEAH!!!
Here's what I did:
(I am on Vista) Control panel - System - Device Manager - Ports - Arduino - Properties - Port Settings - Advanced and changed COM Port Number to COM9. I OK'ed my way out of the properties and then ran the IDE. I went to Tools - Serial Port and set it to COM9. When I did that, it listed COM9 but there was not a check mark which I had seen when I was using COM 3. So I clicked on COM9 and the check mark was added (dunno what that means). I loaded the blink example (File - Examples - 1.Basics - Blink), uploaded it and it ran smooth as whistle!
So, my suggestion is try different COM ports, from 3-9 (I found a note saying Aruduino doesn't like ports above 9).