Когда-то делал. Сложно, ненадёжно. Лучше загружать XP с MBR-диска/флешки, а дальше уже можно нормально работать и с GPT.
Но если очень надо, на том же винрейде есть один из вариантов инструкции:
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Loading Windows XP from GPT disks and accessing space beyond 2.2 TB are possible.
The only limitation is that the system and boot partitions must be entirely within the first 2.2 TB.
Method #1 (unreliable due to errors in the Paragon drivers)
It consists in creating HybridMBR using gdisk (GPT fdisk) and using the driver 'gpt_loader.sys' (Paragon GPT Loader).
HybridMBR is created using gdisk (GPT fdisk) in a special way, so that the BIOS or UEFI of the computer interprets hybrid disk partitioning as MBR and the loaded operating system already as GPT, thanks to the gpt_loader.sys driver (Paragon GPT Loader). For 32-bit driver version 8.0.1.0 there are patches [@hardwarefetish.com] that fix BSOD and high RAM consumption but do not fix file system corruption problems. Driver versions newer than 9.0.5.x are not suitable because they report that "This driver version doesn't support hybrid disk partitioning". Drivers can be extracted from the installers of Paragon GPT Disk Manager or Paragon HFS + for Windows.
Instructions for creating a HybridMBR:
of the 3 available partitions (the 4th slot is used for protective partition) in HybridMBR it is enough to specify only the system and boot partitions;
it is not necessary to specify the remaining partitions in HybridMBR because Paragon GPT Loader driver will subsequently provide access to them;
DO NOT accept the offer of the utility to place a protective partition with the identifier 0xEE in the first slot created by HybridMBR;
DO NOT allow the utility to mark the remaining space with another additional protective partition with the identifier 0xEE.
Method #2 (reliable, meets the UEFI Specification)
It consists in using a special ProtectiveMBR from the SYSLINUX v4.x+ distribution which converts GPT to NormalMBR on-the-fly in the RAM.
Like Method #1 these actions are performed directly on a loaded Windows XP operating system.
for Windows XP SP3 (32-bit) disable Windows File Protection and in the 'system32\dllcache' and 'system32\drivers' folders replace the 'disk.sys' and 'partmgr.sys' files with similar files from Windows Server 2003 SP2 (32-bit) with GPT support;
create HybridMBR as described in Method #1 but additionally assign the Legacy BIOS Bootable attribute to the system partition GPT which corresponds to the active partition in HybridMBR;
on top of the newly created HybridMBR create a NEW HybridMBR with ONLY ONE protective partition with the identifier 0xEE exactly on active bootable partition space (in this case, HybridMBR will be a true ProtectiveMBR);
from the distribution of SYSLINUX v4.x and newer execute the command 'syslinux.exe -m -f C: gptmbr.bin', where 'C:' is the letter of any partition on the target disk.
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