I just bought this new radeon hd 4670 for my old PC hoping to boost my performances while playing games. A friend of mine told me that a new video card wouldn't do the trick because it would be "bottlenecked"?? by the rest of my hardware.
I am currently using a Pentium 4 3.0 ghz with 2 gig of ram. I am not sure what mobo I am using but I do know it supports Pci express 2.0
According to most TH people the Pentum 4 is really, really, old. Think when Blu-Ray wasn't even made yet. You're not sure of the mobo but if it supports PCI-e 2 then I think its modern enough to support a Core 2 processor. However really check the mobo because I don't know of any PCi-e 2 mobo would support P4 unless it's an nForce.
Most Dells have either a visible service tag or name plate on them, failing that check through system information Start>Control Panel>System>System Info although a quick Google shows that motherboard belongs to an Optiplex GX280.
From that search the system board will not support a dual/quad core upgrade, sorry, you're stuck with a single core only.
That HD4670 should run without problems but what are you upgrading FROM?
By 'bottlenecked' your friend means that the CPU cannot feed the graphics card fast enough, slowing it down because it is waiting for the CPU to send it data it can work with.
I know it may seem ridiculous but I got my info from this site. http://en.wikipedia.org/wiki/Optiplex
Anyway its says the chipset is only a 915, as far as I can tell that's even older than my Dimension E520 which uses a G965. That wouldn't support PCI-e 2. It wouldn't just be a bottleneck the highest CPU it could go would be a Pentium D, and that already is a bottleneck as it's a sub-par dual core CPU. I would know I own one.