problem in migrating database

Hi .

I m facing some problem in migrating database from sql server 7.o to oracle 8i,The problem is that when i migrate databse .the table fields of sql sevre 7.0 type VARCHAR convert in to CHAR in Oracle ..is there any way to convert auromatically VARCHAR2 in oracle …
one method i found while using DTC wizard conevert every fields to VARCHAR2 manually.

thanx
jainendra