large drive in xp

By default Windows 2000 SP2, Windows XP and earlier versions of Windows do not support 48-bit Logical Block Addressing (LBA) for drives larger than 137GB as defined in the ATA/ATAPI 6.0 specification.
Fire up regedit, drill down to
HKEY_LOCAL_MACHINE\SYSTEM\CurrentControlSet\Services\Atapi\Parameters

Create a new DWORD value, or modify the existing value called ‘EnableBigLba’. ( without the ‘)
Save, exit and restart to see the full Potential of your brand new 300 Gig Hard drive. It works!

System Key: [HKEY_LOCAL_MACHINE\SYSTEM\CurrentControlSet\Services\Atapi\Parameters]
Name: EnableBigLba
Type: REG_DWORD (DWORD Value)
Value: (0 = disabled, 1 = enabled)