Best CPU for an aging PC

I think you have the best you can in there. A P4 Northwood at 2.8GHz 478 socket is a very nice chip. Newegg has a 478 Prescott that may fit but I am not sure that chip will work in your Dell nor is it better or worth the money as the performance difference would be minimal. If it was in another system you could overclock it. Check e-bay and see if there are any faster 478 socket P4s for sale but it may be tiime for an upgrade.

the best you'll be able to do is a p4 ~3.2-3.4 with hyperthreading. it won't help a whole heck of a lot, though. I had a very similar rig before i started updating. If you want to upgrade for gaming, you're better off just getting a vid card. If you want to improve overall performance, sell it all off and start over. That's what i had to do, but it was a lot of fun and i learned a lot.

i have (now a backup pc and runs my mail server/redirects) a p4 prescott 3.4 478 processor. It works very well still for its age, I cant remember the bencmark values now but was quite a bit faster than my friends 2.8 was.

I also had mine OC'd for gaming for a while, got it up 3.7ghz and added a nice 15-20 FPS stable in HL2 engine games.

But like mentioned above maybe a video card would be the better investment.

I did the same thing with a Dell 4600. It had P4 northwood in it so I bought an Asus P4P 800SE mobo and Zalman 7000 HSF for it. I also bought a WD 160GB SATA 150 HDD and a PC P&C Silencer 360 PSU.

I then put all that into my old Lian Li PC 60 case along with 2x512MB of Corsair XMS I had when I upgraded to 2GB and the old 6800 vanilla that was in the Dell. I added a Zalman 700 cooler to the 6800 vanilla. I overclocked the Northwood easily to 3.2GHz and gave the system to my wife.

Here is the good part. I sold the Dell mobo for about $65 (P4P 800SE was $75) the Dell RAM (2 x 512MB) for $90 (Corsair was $85 new) the Dell PSU for $45 (PC P&C Silencer was $60) and the Dell case for $30. Just about covered the costs.

The CD/RW drive went into the new rig and I used the XP CD that came with the Dell as the OS for the new rig. I had to call MS to activate but all they wanted to know was whether the Dell was dead or not.

Wife was happy as her old HP POS sucked and this thing screamed, I was happy because I damn near broke even and the folks who bought my castoffs were happy as thet got their Dells back up and running.

I've since sold the Northwood and P4P 800SE and moved her to my old A8N SLI Deluxe (with A8N SLI Premium Heatpipe installed) with a 4600X2 and my old 6800GT. The 6800 Vanilla went into my brother's Dell 4600.

Hell, even the environmentalists are happy as I never throw anything out.   I just keep passing it on.