HTML table header height and width

Question

Hi, 
   i am using a table in my application in which i am entering around 20 to 30 columns. for all the column i have given name in the table header tag(<th>) for 3- 4 columns its height will be good after entering larger size text in <th> tag height will get increasing. how to make it constant so that look and feel will be good.
 
if i enter header name as 'create sales order' after entering text it will come like one below the other like create sales  upper side and order in below. how to display in single line? please suggest me how to fix header height and width.


With Regards
Ashwini