Would it be worth it to upgrade this old computer?

When I was a bit younger, i got this old computer for Christmas.

http://www.amazon.com/...001B1CRFI/

Despite its 1gb ram, obsolete operating system and old parts, it is actually a really good computer.

I read somewhere that almost any desktop can be upgraded with additional RAM to dramatically increase the system's performance.

These are a few questions i would like to be answered if possible.

1.) I was planning on upgrading as many things as i can in this computer. If i upgrade the RAM alone, would i be able to turn this old computer into a low grade gaming computer to play games like Minecraft?

2.) I also read somewhere that installing a lighter weight operating system would as well improve the performance of this computer. Is this true? And would Windows Vista or Windows 7 be lighter?

3.) Could you give me a link to some RAM sticks that would be compatible with this computer?

Planet Minecraft not allowing new accounts?

I need to get on Planet Minecraft so I can respond to posts I'm interested in but it's telling me making a new account is not possible? Anyone know what that is about, or is the site shut down in some way?

How well does GTX 660 perform, with i5 4440?

Hi, i would like to know whether the nVidia GTX 660 2GB and i5 4440 would allow me to play modern games on medium-high, like Battlefield and Minecraft, thanks.

Dell Optiplex 720 Graphics Card and Power Supply?

I have a Dell Optiplex 760 DT (Desk Top) that i got for free and i decided to slowly turn it into a decent gaming computer, i need help trying to find the best graphics card for it and possibly a new power source. All i mainly want it to play is Minecraft, Call of Duty Series, Alan Wake, Dead Island, Fallout Series, Grand Theft Auto Series, Zombie killing games, Etc. If you have any other tips about turning my Optiplex into a gaming computer feel free to tell me.
I know that my computer has only one PCIE slot and i would like to find one that fits it with no medications to the case and does anyone know of maybe a 400 watt power supply that will fit my computer?
I've also been looking at these video cards: ATI Radeon HD 3450 and ATI Radeon HD 3470. How good are they for playing the games that i want to mainly play?

Added (1). I have a 2.6 GHz processor, the question is Would i be able to upgrade it from a 2.6 to possibly to a 3.0 if not what would be the highest i could go?

Any minecraft seeds of middle ages?

Does anyone know any minecraft seeds with a middle ages feel to them? Kind of like middle earth or a landscape with a castle or small town. For mac or pc. A seed that has different landscapes like snow lava water forest and desert

YouTube gaming, what games should I play?

I want to start a YouTube gaming channel but I don't know what to play. I have a lot of Nintendo games and i'm able to record them and I also have a gaming PC. I don't like Call of Duty or Minecraft so i'm not really sure what to play.

I want to entertain people so I think that I should probably pick a game that people like.