Question is asked incorrectly.
The maximum HDD supported depends on your HDD controller. For this, you
will need to check with the manufacturer of this (in case of onboard
controller you can probably find this at the motherboard manufacturer).
However, there are 2 types of partitions XP can be installed on, FAT32 and
NTFS, these only defind the max size of a partition, however a disk can
hold several partitions.
Max size of a FAT32 is theoretically 8TB but realworld limit is 2TB.
However XP can read FAT32 of any size, but only create 32GB FAT32
NTFS, which is the preferred filesystem for Windows (NT family) today has a
maximum of 256TB.