This is what you do in Windows 2000 Professional. XP Pro should be the same, although there may be small differences in the routes to certain functions, and the user interface.
Connect your firewire caddy with the disk in. XP should detect the new hard disk.
Use Disk Management. Administrative Tools > Computer Management, then select Disk Management.
Or, right click My Computer, select Manage, select Disk Management.
Wait for Disk Management to load. Once loaded, you should be able to see the new disk on the right hand side in the lower section, a sort of graphical representation with colour (with boxes for different partitions or drives.
If you have only one internal hard disk (which will be Disk 0), the new disk will be shown as Disk 1. If you have 2 internal hdds already, the new disk will be shown as Disk 2 (and so on).
The size of your new disk should be about 111.7 GB in Windows.
See what Disk Management says about the disk. If there's already a partition there (taking up the whole disk), you need to delete the partition first, then create new smaller partitions.
To delete a partition, right click the area of the partition, and select delete. Confirm the deletion.
Then the partition will become unallocated space.
If there are no existing partitions on the new disk, the whole disk will be unallocated space.
Right click any unallocated space and select create partition. Then follow the prompts.
You can select create primary partition or extended partition. Since you won't be booting from this disk, it doesn't really matter. I suggest you create an extended partition.
Then choose the partition size. If you choose to create an extended partition, choose the entire disk space. Then you can create logical drives within the single extended partition.
After creating an extended partition, right click the extended partition and select create logical drive. Specify the size. You'll be prompted to format the disk, choose the file system (NTFS or FAT32), Volume label, and so on. Make your selections, click OK, and the new logical drive will be shown in Disk Management.
Don't leave Disk Management yet, as XP will format the partition in the background. After a little time, you'll see in the box for the logical drive you've just created, the progress of the formatting (e.g. formatting 28%). When it's done, you can create further logical drives in the extended partition.
If you choose to create primary partition, same. You'll receive the same prompts as for creating a logical drive.