Follow the instructions above and install the Excel viewer under wine or some other virtualization software (I use Sun virtualbox). Open the xlsx file and do the copy-paste trick to openoffice.

Alternative (and perhaps better) solution: Get version 1.1.7 of odf-converter which will handle xlsx (as well as pptx and docx, of course) files.

And promise not to swear and curse at the stupidity of folks out there using MS Office 2007.

I.