At first you can Tikisheet. It's a new module and very interesting too.
There is also the hard way:
1. Save the EXCEL file as CSV.
2. Open it with an editor like Notepad and replace ";" with "~|~".
3. Copy and Paste all the contents of the new file into a Wiki page.
If there is no merging cells or other special formats everything will be fine!!!
Maybe you 'll have a problem viewing all of the Wiki page if the rows of your file are too many. Try and check.