How to completely erase a hard disk

[Juan Pablo Mazzini]

I`ve made a mistake instaling an Ubuntu 7 server with RAID disk 1.  
Now when i try to install again de instaler is unable to make a new  
raid cause the old one is still configured somewhere, anyone knows a  
metod taht i can use to put both hard disk in like new and erase all  
the information stored in them including the booth sector in order to  
install again.

regards
Juan Pablo Mazzini
Argentina