The old fashion way to do this was to manually change your boot.ini file on the original C: drive to have an extra entry for the second disk and you would select the one you wanted at boot time. I could give you instructions for that but I'd have carpal after I was done. The easiest way to do this is to go to recovery console and use the bootcfg command.
To use the bootcfg command, start the Recovery Console with the Windows XP CD-ROM, and then choose Recovery Console.
The bootcfg /add command scans the computer for operating systems and then displays the results. From this location, you can add an installation to the Boot menu.
You may receive a message that is similar to the following message:
Scanning all disks for Windows Installations
Please wait, since this may take a while...
Total Identified Windows Installs: 2
[1] C:\Windows
[2] D:\Windows
Select installation to add: (select a number)
Enter Load Identifier: (You can put any unique identifier you want here)
Enter Operating System Load Options: (leave it empty for now and ask me about this later)
This process adds a new entry in the Boot menu. When you add an installation, the bootcfg command also makes the installation the default operating system boot entry. You can change the default by editing the boot.ini file.
BET YOU WISH YOU HADN'T ASKED HUH!!!!!