I currently have a 2.4ghz AMD 64 processor... I'm thinking about purchasing a P4 2.8ghz. I know a lot of people say AMD is better, so I'm curious if there is actually a difference between these two, or is an AMD 64 so much better than P4 it'll just kind of even itself out, and make it not worth my money to upgrade...

Thanks in advance for any advice...

2.4ghz and 2.8ghz is a very small difference. I would be surprised if you even noticed because not many people would. Also AMD is one of the most well know processor brands in the world and your motherboard might not even take that type of processor. Personally I would stick with what you have and not waste the money. Unless of course you are buying a new machine but the processor itself there is no need.

Right now I have an e-machine, AMD Athlon 64 Processor, 2.4Ghz with 1gb Ram. The computer I'm thinking about getting is a Dell P4 2.8Ghz with 1gb Ram... I can get the Dell for $100 if I want it.

In a word DON'T!!
The Intel P4 is an antiquated chip and as such doesn't have the performance of the, much newer, AMDx64.
You CANNOT simply compare clock speeds with AMD and Intel chips as this is completely meaningless due to the different chip architecture used.
In tests an AMD chip of the same clock speed will out perform the same speed Intel.

Also the P4 is a 32 bit chip, while the AMD is a 64 bit chip.

Thanks guys, I'll save my hundred bucks :) Or maybe buy the P4 for a hundred still and sell it for two... hmmm... :)