You can simply copy-and-paste your files over to the new drive without a problem. However, programs are latched into the system registry and use shared system files throughout the installation. Thus, you can't simply copy them over.
Some programs, such as AlohaBob PC Relocator claim to be able to do this, but their efficiency is limited. Some software, such as Microsoft Office 2003, is designed NOT to be movable to prevent piracy, so the only solution is to install from scratch using your CDs.
I have a dilemma. I have a Windows XP system now on one HD and a Window 98 system on another HD in two different computers. I am trying to find out how to get all of my programs/files off the Windows 98 HD onto the Windows XP hard drive. What is the simplest and quickest way to do this?