Hi kielon,
1. In LyX, insert a table with the same dimensions as the one in the excel.
2. Place the mouse cursor in the top left cell of the table.
3. From the menu of LyX, choose Edit → Paste Special → Plain Text, Join Lines.
I took the above from
http://www3.nd.edu/~zzhang4/doku.php?id ... cel_to_lyx which in turn was linked to from
https://twitter.com/imLinJ/status/394782205022437376
However, note that is never I good idea to paste. You should link the two documents so that if you change one the other is automatically updated. You can do this with an Excel spreadsheet if you have Gnumeric. In LyX, go to Insert > File > External Material and use the Template "Spreadsheet".