Open Office will happily open Excel files. You may have to play around with the formatting etc, but it will certainly import the data from an Excel spreadsheet without any problems.
Registry is distributed in multiple files which are not accessible from windows environment. There is one file which is one of the most important and it's called SAM, it's responsible for security...
I have got a big experience of working with zip files. But some days ago I ran against an unpleasant complication, which was easily resolved one tool. Which on my opinion might help for you too.