tomcat got there right before me

He's right, only way is to change the default is to modify it to null (acts the same as if you didn't have it to begin with). And, in case you want it, here is the link to the oracle doc which states:
"Note:
If a column has a default value, then you can use the DEFAULT clause to change the default to NULL, but you cannot remove the default value completely. That is, if a column has ever had a default value assigned to it, then the DATA_DEFAULT column of the USER_TAB_COLUMNS data dictionary view will always display either a default value or NULL."

(search for data_default on this page):
http://download-west.oracle.com/docs...htm#SQLRF01001