|This is a hardware or CPU question, not an XP question.|
The P4 Northwood runs at 533MHz FSB with a multiplier of 21x. The 2.4GHz Celeron runs at 400MHz FSB with a multiplier of 24x.
One of two things is going on:
- either your motherboard doesn't support 533MHz FSB so it's defaulting to 400MHz FSB. 21 x 100MHz (400MHz FSB) = 2100MHz
- or your board does support 533MHz FSB but you didn't change the setting.
You should ALWAYS check the motherboard's CPU support list before buying a new CPU.