How do I download XCode4 from the Mac App store

Question

I initially posted this at the Developer forums, but I chose the wrong forum to post in, and so I was directed here.
Original message
It failed a few times during the download but when I restarted it it started again from where it left off. This was good.
However the last time it failed it changed something as when I retry it now it starts from scratch.
It took me about 3 days to almost complete the download so I don't think I am going to successfully download a 4.5gigs XCode file
without any download interruptions.
I have tried copying the pkg in Library/Application Support/App store so that I can get it to start from where it left off. However whatever I try it always seems to go back to 0 bytes when resume is clicked. This is a trick I learnt in Firefox that I used when downloading previous XCode versions(xcode3). However this does not work for me.
Thank you
Next message
Does the app store use the http protocol for the download? If true then I should see problems with resuming downloads in other applications(eg firefox). I don't see those problems.
How often does the app store commit the data saved so far. Or what size download chunks does the app store save? 100k 1MB 10MB?
I have tried to resume when I had >1 Mbye saved, and it just started from 0.
Next message
I have just tried downloading xcode3 from developer.apple.com using firefox, and the resume in firefox works fine, even after a firefox restart.
The app downloader had over 4gigs worth of data saved, then there must have been some problem, then the amount of data saved must have gone back to 0.
How does the app downloading program decide to zero out the saved file data? Is there any way to inflence this or somehow make manual backups, like I could with firefox.
I do have broadband, but its a slow broadband. I did have to reenter my username and password a few times during the download process, probably because there was some sort of cookie expiry happening. However this worked fine.  However something went wrong at the end. maybe it was because I clicked the retry in the pop up, rather than the retry next to the app store download progress bar.
If there was a flag or something that said whether or not to resume or retry from scratch then I could maybe edit that and it would help.
What happens now is that when I click pause, the data is written to the .pkg file, which is correct.
However when I click resume the file size immediately goes back to zero.

Answer 1

I tried it again, and this time when I resumed it lost about 10Mbytes, so I guess this means that the app store downloader saves its data every 10MBytes.
I will try downloading the whole thing again(XCode4) and just hope that this time I can get the whole download before it decides to wipe out what it has already downloaded.