JDC & Roobubba:
Hardly a n00b question -- actually, very good points are brought up.
I. Compression vs Overdrive
Without getting too detailed prior to my 1st cuppa joe today, compression and overdrive are two different effects and will give you different results.
Overdrive amplifies your guitar's signal going into the input stage of your amplifier causing the preamp to distort. On its own, an overdrive pedal does not contain much actual distortion. For this you would use a distortion pedal. That is why both a clean boost and overdrive will yield very similar results. (I'm oversimplifying the case here and can/will go into more detail about even/odd order harmonics, etc if you want)
General rule of thumb 1:
More preamp gain = less gain in front of the amp (overdrive/clean boost)
Less preamp gain = more gain in front of the amp (distortion pedal)
II. Does a compressor overdrive the amp, or does overdrive compress?
The short answer -- yes. But how they do this is different.
An overdrive blunts the actual soundwave, limiting its dynamic range into a kind of comprression, but it is not nearly the amount of compression you get from an actual compression unit.
A compressor severely limits the dynamic range of the signal prior to it hitting your amp's input stage.
Most compressors have an output control that may or may not overdrive the input of your amp (depends on many factors), but that signal is already compressed prior to reaching the amp's preamp stage; ie, not being compressed by the preamp. This sounds totally different than the type of compression you get from an overdriven preamp stage.
General rule of thumb 2:[/color]
Overdrive causes the preamp stage to compress by limiting the dynamic range of the input.
Compression limits the dynamic range of the signal prior to the amp's input stage allowing more clean headroom.
III. What about an EQ through the FX loop?
Running an EQ through your FX loop adds more output to the preamp stage; this will yield an overall level boost; for example, for use as a solo boost. Using an EQ or clean boost in the FX loop are very popular choices for an ad hoc solo boost.
General rule of thumb 3:
NEVER PUT A GAIN INDUCING DEVICE INTO THE FX LOOP OF AN AMP! That includes overdrive and distortion pedals.
I hope you find that helpful!