Installing RAM and hard drive. Motherboard capabilities?

I read an article below about External Hard-drive purchase. I got aa lot out
of it, and will read more later, but it is along the lines of what I need to
ask.

If you need any info from me, please ask and tell me where to find it.

I plan on installing as much RAM and hard drive as I can in the shorter-term
so I can archive my music collection and dvd's. I actually would like to
install what I can internally instead of externally.

I have 32-bit XP, 1GB ddr2 memory (RAM?), and AMD Athlon 64 X2 Dual Core
Processor 3800+ 2.01 GHz, 768 MB of RAM on an Acer ASE380-ED380M.

I opened my computer up last weekend. I saw the SATA hard-drive and 3 other
potential spots for more hard-drive. I want to fill 2 or 3 with SATA, but saw
PATA drives. I don't know what PATA is, but it's bigger. Can my system handle
it? I'm going to start getting 2 or 3 terabytes (or more). I have lots of
music, dj for fun, but I also make music and need space.

I noticed that there was a certain kind of small black plug connected to the
hard-drive from the back of the computer with lots of wires comming out of
that. It was split (connecting to the hard-drive there) and one is free for
one spot (not the three like I want). I noticed on web-sites there are
certain kinds of power cords for sale and in my computer tower it appeared
that my dvd-drive was connected to a white plug (not the small black ones,
but that bigger white connection went into the back of my computer too), on
that white plug it connected to the dvd-drive and could be dissattached. But
the dvd-drive connector did not block any more connections, it continued it
(something else can be plugged in still). Can the small black plugs do this
too (connect to each other and keep the chain going)? Or am I limited to the
two connections for hard-drive?

For the RAM There are 4 ports, in two there were 2 - 512 chips, the other
two were empty. Do I have to have a specific kind of RAM? I know sometimes
some computers can only handle some amount or kinds of it.

What is in the back of my computer tower? It's where the plug-in for the
electrical outlet goes, and everything in te tower connects to. Is this my
ADM Dual Core Processor? Or is the processor the motherboard with all those
diodes, and ports (it's on the side and covers it. It's the big thin piece).
Can this thing in the back of the tower be replaced? Are they usually left
alone?

What can I put in the back of my computer where these PCI local Bus ports
are? I have 4 slots. 2 large ones, one small and one square (I think, or two
smaller ones). One has a modem in there I don't use (a line in can be seen),
the other three are free. Can this make my system 64-bit, or is it needed to
install stuff to accelerate my computer? Can I put more memory or a graphics
care there or something?

Lastly I figured I can fit a small drive and another dvd/hd burner/reader of
some kind in front. But that can wait a bit.

How can I find out the lmitation on what kind of computer I have (what the
motherboard can handle, or the processor, etc. Eg: Some items cannot be
installed into older computers (mainly due to not having the right
connectors, ports, etc). I don't want to buy something that is too advanced
for my computer to read or run with.

I just want to learn and to install what I can myself.