How much CPU can I upgrade? Dell Dim 4400

I have a dell Dimenssion 4400. I want to upgrade the CPU. How far can I go?Service Tag: CQRGG11 System Type: Dimension 4400 Ship Date: 5/24/2002 Dell IBU: Americas Quantity Parts # Part Description 1 8P779 ASSEMBLY, CARD (CIRCUIT), PLANAR (MOTHERBOARD), DIM4400, AUDIO, REV1 1 9K795 PROCESSOR, 80532, 2.0G, 512K, 400FSB, SOCKET N 1 2M612 KEYBOARD, 105, 6P, NORWAY/NORWEGIAN, NMB, RUBBERDOME, MIDNIGHT GRAY 1 1K578 MODULE, DUAL IN-LINE MEMORY MODULE, 512, 266M, NON-ECC 1 68KYG MODULE, FLOPPY DRIVE, 1.44M, NEC CORPORATION, DIMENSION, CHASSIS 2001 1 2K928 MODULE, HARD DRIVE, 80GB, I, 7.2K, CHASSIS 2001, WD-XL40 1 3K542 MODULE, CARD (CIRCUIT), GRAPHICS, 64MB, NV11, Television I have upgraded the Grpahics to a GeForce Ultra 9800 since.As per this site.. http://www.powerleap.com/I can go up to a3.00 Ghz. 1. Would this be worth the upgrade? I have a great Video card...but the CPU seems to be the weak link.2. Any problem I should anticipate..in opening my computer... Pulling the old sucker out and plugging in the new one? would I have to do anything else?3. Would the Win 2000 OS regitration think..that this is a new computer and freeze on me?