This question is for someone with experience in post-production audio
editing for films/videos.  What is the best way to match dialogue
recorded later (ADR) with dialogue recoded on location?

The audio recorded after the fact is much louder and has a "deeper"
sound. I've already tried messing around with the volume and EQ (I use
a paragraphic equalizer in sound forge) but I still couldnt get it to
match. Im sure there is a way to do it, I know that studios do it all
the time.

I am using Sound Forge. I have several plugins and access to many
more. I think I have all the tools I need to do what I want, Im just
not sure exactly which tool (plugin) to use.

Also, it may be important for you to know that all of the "on location
audio" was recorded outside. Some of the stuff that I recored after
the fact was in a studio and some of it was recorded outside (in a
quiet place), but the microphone was closer than the on-location
stuff, so it doesnt sound the same. The microphone Im using is a
Sennheiser me66.

On a related note: Im interested to know if there are some general EQ
settings that I should have on all the audio of my finished product to
make it sound better (for example, cutting out the very high and very
low frequencies to get rid of excess noise without interfering with
the sound of the actors' voices)

Hi, djfimls !
I've held off answering hoping that someone with a detailed knowledge
of Soundforge would be able to help, but since no-one has, I'll
elaborate on my original comment.
Soundforge appears to be an excellent tool for music, but for video
you might like to take a look at their other specialised product at:
VegasŪ Video LE 3.0 </PRODUCTS/showproduct.asp?PID=416>, Sonic
Foundry's professional digital video and audio multitrack editor

Sound for film is usually recorded on four or five tracks, two for
voice, either one or two for music, and one for ambient noise.
Since every location has different acoustic qualities and different
background noise (traffic, wind, birds etc.) the last thing the sound
engineer records in each local is an "ambience " track. The actors
remain on set, but do not speak, while twenty or thirty seconds of
sound is recorded. The actors are there because the slight rustle of
clothes in small movements, or the shuffling of feet in a school hall
or church scene, are part of the ambience. It's amazing how much sound
there is in "silence".
This ambience track is used behind any post-recorded dialogue in order
to make it sound as if it was recorded on the location.

As you yourself point out, microphone distance makes a big difference.
Usually this is measured and noted on location and reproduced in the
studio.

For best results I suspect you will need to rerecord the studio
dialogue, reproducing the microphone distance as closely as you can -
and of course using the same microphone and recording equipment - and
if you do  not already have an ambience track from each location you
may need to return there to make one. It does not have to be long, and
of course there is no need for camera set-ups, so it should not take
too long.

Using a De-esser to reduce sibilance in speech can be very useful. EQ
settings are best set for each individual voice.

Good luck with the project.