I have a Dell Dimension 4700 and I was wondering if I would be able to upgrade the processor to an Intel i5 2320? It's currently running a Pentium 4 530 Prescott 3.0GHz w/ HT. I'm using the same motherboard that came with it from Dell.
Web surfing, watching online HD video, Excel, Word, watching DVDs, etc. Very little gaming.
For that use, an i5 is going to be overkill.
A home built system is always going to have better quality components, but is going to give the best value for gaming and 3D/2D rendering/editing.
For your use, a prebuilt will be fine. I didn't ask your budget range, but anything with a core i3 or the AMD FX-4100 or quicker will support you for a few years for your use.