Oracle 9i, Undotablespace error

sir,
Im new to oracle development. im using vb6.0 and ora 9i.
and i have the following problem. pls help me to resolve this problem.
The undotbs01.dbf file sizez 8.5 GB. and my oracle didnt allow me to log in.
my partition size is only 9GB. I installed oracle only a month before.
I try to make a backup of undotbs file. but i cant able to copy.
my oracle didnt allow me to login to make any query.
I tried using sys as sysdba and / as sysdba , but it didnt work.
How to solve this error. Pls somebody help me to resolve this issue.

Can i able to create a new undo tablespace?


Balamurugan.M