I am currently using the Celeron setup, and after 2 years it is so cluttered and junked up I think it's time to start fresh. Would it be better to switch to the P4 with more memory? The only disadvantage I see is the slower board clock and primary cache... but I don't know if those will make a huge difference.
My question is how much will this switch cost you? If it will cost $400 or more, you're better off building a new system. Overall, The P4 system is faster. I will warn you that with Office, the web, Outlook, and the everyday stuff, don't expect a huge improvement. However, in Photoshop, you will see a difference.
Well if you have to pick between the 2 I would go for the p4 system. It has more ram and since you will be multi-taksing it would run alot better for you. Also how much if any will you be paying for the p4 system? If you are spending any amount on it, say 300-400 you can build a more up to date system to do office type applications.
You have the rare SL7EY Northwood? Wow. Anyway, if the Celeron is a Celeron D (Prescott) I would simply overclock it (if your board supports it), it should be fairly easy with the proper cooling (if you have it). Prescott Celerons should easily be able to 3.6-4.0Ghz with the E0 or G1 core. If overclocking is not an option you may be able to do a BSEL mod to make your Celeron run at 3.8Ghz on a FSB of 800MHz.
Edit: Obviously it's a Prescott Celeron, because they're the only ones with 533 FSB. Duh. Northwood Celerons ran at 400 FSB.
I would go for the P4 2.8GHz and OC it. You will notice a huge difference. When I changed out my fiances 2.7GHz celeron for a 2.8GHz P4 itt made a world of difference for her crappy eMachines. I hav since retired that computer and am thinking of taking it to "PC heaven".
I think you're mistaken about the P4 bus speed, the celeron runs at 166Mhzx4 = 533Mt/s, the P4 should run at 200Mhzx4 = 800MT/s. On this processor you probably also have hyperthreading. The 512k of cache tells me it's a Northwood too.