There's actually an advantage to doing it from within the install. You can format OR repartition within the install plus you don't have that extra reboot due to 'new drive letters' yada yada...
BTW, if you take an existing XP install, run sysprep on it, shut down and then drop it into new hardware (mobo etc..) you'll be up and running no problem. The only limitation comes if you jump HALs but if both systems are built in the last several years you'll be sticking with an ACPI hal.