How much money would it cost me to build a good computer?
I want to use it for photo editing with Photoshop etc., business programs, playing music and internet browsing including video watching like youtube, all open at the same time.
I would like a very good but not top of the line system. I would like to max out the sweet spot where spending more gets a lot of bang for the buck, but before the point where it costs a lot more to realize relatively smaller improvements.
The only parts I can probably use that I already have are monitors, a 250G SATA HD (not SATA2) and optical drives. I have 3G of Ram but it's DDR not DDR2.
I used to buy Gateway and then Dell because they included lifetime tech support for very little cost. Now they charge about $400 for a 4 year maximum. I don't want to pay that much--so since I'm not going to have their tech support, I might as well build my own computer. I'm on about my 5th computer now, a Dell Dimension 4600 w/ Intel P4 3.0GHz HT.
My first computer was a Gateway 386 25Mhz which was second only to the 33MHz units that were available. It had a 40MB hard drive and I forget how much RAM. 40MB was a big HD at the time, as most people only had 20s. However, I knew a major geek that got a 1G hard drive shortly thereafter. He paid $1000 for it. My whole system cost me $3000 with a 13" color CRT, although I added a math copressor for an extra $300 later.
I specced out a system for a friend of mine (who wants to do the same things you do) and it came to about 700 dollars. That is just the system, and included a low end dual core AMD cpu, a low end ATI video card, a crossfire motherboard (he said he wanted to use four monitors down the road) and 2 gigs of DDR2 ram.
You mentioned monitor(s) plural... if you're fixing to run dual monitors it'll be slightly more, but doesn't have to be a lot more.
In my opinion, for what you've listed you could get a pretty sweet set up for 5 or 600 bills. That's just an estimate, and is on the low-end. Beyond that it will depend on what you specifically want for parts and so on.
Keeping the hard-drive isn't a bad idea, it'll save both time and money in the long run... although depending on your budget you may want to look at this hard drive... I've been told that 320GB is the "best bang for your buck" so to say, and after 1684 sales on Newegg, I think that says a bit.
As for your ram, you could keep it, but then you'd want to find a motherboard that took DDR and DDR2 in a day where most people are gearing up for DDR3 anyway...
Depending on how much you do in photoshop I think 2GB DDR2 would do you just fine. As for other components, video card and CPU and such, that will come down to how much you are willing to spend on each, you shouldn't need much of a video card to power business apps and such, there's a nice C2D you can get for $117 here. or if you didn't want to spend so much on the CPU right off the bat, you could always go with something like this and then upgrade later on (July 22 has big price cuts coming, not sure when you're planning on buying, or what your budget is)
Beyond that I'm not sure what to say really, it'll come down to your budget.