Just in case, Microsoft says a foreign disk is:
The Foreign status occurs when you move a dynamic disk to the local computer from another computer running Windows 2000, Windows XP Professional, Windows XP 64-bit Edition (Itanium), or the Windows Server 2003 family of operating systems. Foreign status can also occur on computers running Windows XP Home Edition that are configured to dual-boot with another operating system that uses dynamic disks (such as Windows 2000 Professional or Windows XP Professional).
Dynamic disks are not supported on Windows XP Home Edition or on portable computers. A warning icon appears on disks that display the Foreign status.
It does not look like that adding the disk to your 'system configuration' will harm it in any way*. It should be completely harmless to do and your data should remain entirely in tact. That said, you should always be making backups of any critical data. See Microsoft:
To access data on the disk, you must add the disk to your computer's system configuration. To add a disk to your computer's system configuration, import the foreign disk (right-click the disk and then click Import Foreign Disks). Any existing volumes on the foreign disk become visible and accessible when you import the disk. For instructions describing how to move and import disks, see Move disks to another computer.
If you are on Windows XP Home, you cannot do this. The only way for you to use the disk again is to erase all of the data from the disk, and convert it to a basic disk:
- Right-click each volume on the dynamic disk you want to convert to a basic disk, and then click Delete Volume for each volume on the disk.
- When all volumes on the disk have been deleted, right-click the disk, and then click Convert To Basic Disk.