Ford Focus Sound System

[XR6 JET]

I've recently purchased my second Ford, 2004 Ford Focus Sedan. The headunit in the car currently a Alpine CDM-7874EB which is great but the downside is that it can't play MP3 CD's. I wanted to know if I purchase a new headunit is it just a matter of taking the old headunit out and putting the new one in or is there much more to it, I'm not really good with electrical things so I think it would be better getting it installed professionally. And do the factory speakers have RCA connections, asking that as I think (might be wrong) most of the headunits have RCA speaker outputs.

[~Spyne~]

RCA connections are only used when connecting the source (cd player) to an external processor, or more commonly, and amplifier. From there, it's always still just speaker wire that then connects to the speakers.
So if there is no amplifier currently installed, it will be speaker wire straight from the cd player (as 99.9% of cd players have BOTH speaker outputs and RCA outputs) to the speakers.

As far as swapping to a new headunit goes, it depends - if u buy a new Alpine, it's quite possible it will just be a straight swap, if a wiring harness was used in the previous install. Because the 7874 is a reasonably old cd player, you may however need to get an updated harness.
If you switch to a different brand, you'll likely also need a different wiring harness.
In ANY case, i would take it to a professional. (If there's no wiring harness at all, and factory wires have been connected directly to the cd player loom/plug, this could actually prove easier in terms of knowing which factory wires are which, but would be more fiddly in disconnecting and hooking up to the new cd player)