I bought the book Simply Rails 2 and I would like to follow along with everything so I can get the most out of it. I downloaded InstantRails as per the instructions, but when I enter the command

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gem update --system
I get the following error message:

ERROR: While executing gem ... <Gem::RemoteSourceException>
HTTP Response 302 fetching http://gems.rubyforge.org/yaml

I have tried turning off the firewall and still no luck. I also tried just installing ruby via the one-click installer, but when I try to use cmd to check even if it's installed --

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C:\> ruby -v
I get this error message:

'C:\' is not recognized as an internal or external command, operable program or batch file.

How can I fix either of these problems?