If you're worried about viruses, just get a mac.
A used Mac on a $500 budget is going to give him an older Macbook or a Mini most likely and that's staying with the Intel machines. I wouldn't recommend anyone that uses current software to buy a PPC Mac. I think the only way the OP can afford a Man on $500 is an OSX86 install and at the point he's show his skill level to be (example below), I don't think that's a viable option.
There's 10 pages of research materials here. You're a guy and you've been using the computer for how many years? How hard it is to not understand what a computer need or doesn't need? If you don't understand HOW to built one, that's fine, but you don't even understand what a computer need for it to run? Look at my post and Ballistic post when we suggest a built, it's always the same types of hardware, just different brands. I seriously don't think you actually want to build a new computer, or even buy a new computer.
I don't know what a dual core processor is. All I know is the bigger the gigs on a ram the faster it processes. The bigger the hdd the more memory. all the lingo youre using is confusing to me. I'm not a computer guy. And I never wanted to build a computer I just wanted to buy one. You guys were the ones who kept telling me to build one. So get off it.
Quick lesson.
A processor processes. It has switches that are either on of off. 1 = on and 0 = off.
Binary, the most basic computer language is 1's and 0's together to make characters. So for example, 000001 is one, 000010 is two, 000011 is three, 000100 is four and so on. This controls everything that you do passes through the process. So somewhat recently, dual core processors were invented and released into the wild. These have 2 cores on them that process the number. Quad cores have 4. What this means is that previously, when you had 5 programs running, they put all the information through one core. So if you did a batch process in Photoshop while transcoding a movie, they would both be fighting for usage in the single core. With dual cores (as long as the programs are optimized to work with dual core chips) the two programs would use separate cores for their processes allowing things to work at the same time at the same speed without fighting for resources.
RAM is Random Access Memory. the HDD is the Hard Disk Drive. It's important to know about both of these to understand how they work. RAM is like an HDD. All it does is store programs and information. RAM doesn't process anything. The difference between RAM and an HDD is that RAM is super fast in comparison. The computer can put an active program into ram and pull it out in what we perceive to be immediately. Up until the advent of Sold State Drives,
all hard drives had moving parts. The rate at which data is pulled from the HDD is much slower than a RAM. Windows 7 pre-loads programs you use a lot into RAM. If you open MS Office Word and it's pre-loaded into the RAM, it opens in a couple of seconds. If it's loaded from the HDD, if cane take 10-20x's longer or more depending on the computer.
A lot of times the HDD becomes the bottle neck in the system. The SSD drives that have no moving parts are helping to fix this though.