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.
