Are there any motherboard upgrade limitations?

I will start with saying that I have an old motherboard - I have an M3A78-CM (AM2). Say, if I wanted to upgrade my processor to an intel i7 I couldn't do that because my motherboard won't support it, right? Okay, I have two questions to ask.
1. If I buy a new motherboard and replace it with the older one, will all my RAM, CPU, GPU and other stuff be recognized by a newer generation motherboard, since you can pretty much see that I have a fairly old system configuration.
2. I don't know how to put this, but can somebody find me the maximum, high-end CPU that THIS motherboard can support? I'm sorry but I don't really understand much about motherboards.}
Oh... and one last thing. Can THIS processor be supported by my motherboard? And how good is it? Thank you for your time.

If you get a new motherboard that is anywhere near a recent design and model, it will NOT use DDR2 RAM, which is what you have now.

You'd need to buy DDR3.

I don't know much at all about AMD processors, so can't identify the strongest processor that can be used on your current motherboard.

But---the rule of thumb is to NOT spend a lot of money putting new stuff on really old motherboards. You are generally better off replacing the motherboard, RAM, and CPU unless you are really restricted by budget.

It is possible there is a relatively cheap AMD processor that would be a worthwhile significant upgrade for your motherboard. Someone else will have to answer that.

Nobody still hasn't answered my first question...

Q1. If I buy a new motherboard and the older one replaced, will all my RAM, CPU, GPU and other stuff be recognized by a newer generation motherboard, since you can pretty much see that I have a fairly old system configuration.

An AMD motherboard can only accommodate an AMD CPU and so does an Intel motherboard can only accommodate an Intel CPU given that the number of pins on the CPU remain the same. An Intel 172 pins CPU will fit into an motherboard for 172 pins CPU so does an AMD. 1117 pins CPU for 1117 pins board.

Your RAM sticks and other hardware can only be used if the new motherboard can use these items or backward compatible. If not, you will have to discard and buy new items that meet the specs of your new motherboard. It is the motherboard that call the shot, not vice versa (the RAM sticks and other hardware).
Sell all the older parts for cash if the older parts are no longer useful to used parts dealer

Rules of thumb for buying a new mobo or motherboard
A.Estimate how much you can afford or spend
B.Determine the CPU you intend to buy or use
C.Determine the new mobo or motherboard
D.Look at the specs of the new motherboard
E.Calculate all the costs
Sell all the older parts for cash if the older parts are no longer useful to used parts dealer