Er. Office 2010 isn't in Beta format YET... There's an invitation only preview build that was made available. As such, you might try checking with the folks in charge of the preview program as to why you're not getting anywhere with it.
In the mean time, you might try the usual fixes for this sort of problem -
Clear your IE cache and history. Delete all temp files.
If all else fails - Reset IE 8 by pressing the ALT key, clicking on Tools | Internet Options and then clicking on the Advanced tab. Click the Reset button at the bottom. This will reset IE 8 to it's default state. All add-ons and passwords will be lost, but it might be worth a shot.
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