It has been a pain for me to make this 2.x GB XCode download successful with my slow ADSL connection. When I first tried, it was broken at over 1 GB then again I had to start over again. Finally with help of apple forums and Google I was able to stick to a successful method. In this case you have to start your download in Safari, and if its broken you can resume it anytime by following a little trick.
1. Login with iPhone Developer account in Safari Browser and start your download. In case you break the download, which would definately happen in a slow connection that takes around 10 – 12 hours to complete.
2. Once it’s broken Right click on broken download and click Show In Finder
3. You will see a file with ‘xcode_3-1.2.3_and_iphone_sdk_4x.dmg.download’ like some thing. Right click on that and click on ‘Show Package Contents’
4. Safari keeps a Info.plist file with download progress that is the one we are going to use for our purpose. Open it with a text editor and notice there’s key value pairs. Notice the key value pairs below.
5. Now you can’t resume this download, that has lots of bytes already downloaded.Do this to use the already downloaded file.
6. First start a new download again in Safari and stop it. Then again go to finder and ‘Show Package Contents’ of this new download.
7. Here also you will see an Info.plist file open it and copy the Download Entry Identifier value.
8. Hay now you are done, paste this to the old Info.plist file. Go to Safari you will see that your old download is now resuming. Saves a lot of time for you on a slow Internet Connection.
Have fun with XCode then.