I was wondering is it possible to expand an existing RAID 1 to twice its size with another pair of HDD's. with no software or OS reload. Windows Server 2003 operating system, If it can be done can someone give some documentation on how to do it.
Yes you can. The feature is called Online capacity expansion (OCE). For step by step instructions, see Intel® RAID Software user's guide, page 120 "Add a Drive to a Virtual Disk".
After completing the steps you can either extend your existing partition or create a new partition with the additional space. See How to extend a data volume in Windows Server 2003, in Windows XP, in Windows 2000, and in Windows Server 2008.