If you're getting that warning you need to keep refreshing multiple tabs in IE - you WILL get a key with perseverance!
If you can't DL past 500Mb, you may be DLing from a dodgy source or there is an issue with your connection/PC.
Good Luck.

EDIT: Just get it HERE

I'm using the direct link to the download at microsoft, no dodgy downloads and no connection problems (wget can't continue downloading after several retries)

//edit: this works flawlessly: http://www.neowin.net/news/main/09/0...ows-7-beta-key

Neowin link does indeed do the trick! thanks