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/eMachines-Athlon-250GB-DVD%C2%B1RW-Vista/dp/B001B1CRFI/ref=sr_1_16?ie=UTF8&qid=1398255290&sr=8-16&keywords=eMachines

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?

Thank you so much ahead of time!

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