You are running 32-bit Vista and any 32-bit MS Operating System can only see up to 3326mb of RAM. A 64-bit OS will allow you to see 4GB and beyond.

There is no problem here

Also there is a thing called page file it works with your hard drive so it will always show less than what you already have plugged in.

No need See above.

How come at one point of time, this same exact place showed 6000-something MB when I had 6000-something inserted. But I took it down to 4, as somebody pointed out to me, that having more than 4 GB installed on a 32-Bit Windows Vista, will actually slow my performace down. So I took out 2. But now, as I remember I did run some kind of command in my "Command Promt" or in "RUN" - don't exact remember in which. Should I try searching for that command again??

There is some command I entered as an administrator in my "Run", and it enabled the use of all and saw all. I found this command on Google. Do you know what I'm talking about, or should Google again??

Yes there are commands and programs that will show you "all" of what is plugged in. But what is actually being utilized by your computer can be found in the my computer properties. Just because it shows in certain spots that you have 6000 mgbt doesn't mean it's utilizing it. As stated above (don't mean to sound like a broken record) 32 bit operating systems only use 4 gigs and 64 can use 8 gig and vista 64 bit can use up to 16 gigs.