You won't be able to do it with just HTML and Javascript. I'd recommend trying Fancy Upload, a MooTools plugin for multiple file uploads. It uses a mixture of JavaScript and Flash, but degrades gracefully. It works with all major browsers including IE6 and there is also a Flash 10 compatible release available for download (though the demo hasn't been updated yet).
Update (2012-11-26):
Multiple file uploads are possible with valums or blueimp file uploaders.
For recursive directory uploads, your best solution is using Chrome 11's new folder upload API. It also seems to work on Firefox if you use a vendor prefix.
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