First an important note: when typing a date into a cell you can't type it with dots like 12.1.2008 (Excel won't understand that as a date) but you have to type it with slashes: 12/1/2008
now for your question:
You can format the date in a cell as you desire by following the next steps:
1. Select the cell(s) containing the date(s).
2. Open the menu "format" and choose "cells".
3. On the list on the left choose "custom"
4. In the "type" text field you will see something like m/d/yyyy , delete it, and type the following instead: dd-mmm-yy
5. Click OK.
The key here is the dd-mmm-yy which sais to Excel: give me the day in two digits, the Month in a word, and the year in two digits.