Problem instralling gems

I have problems installing gems on my ubuntu 7.04 machine. i haver
installed ruby 1.8.6 and rubygems 1.0.x. I am directly connected to
internet. When i try to install the gems , it throes some wierd errors
sucha as:

ERROR: While executing gem … (Gem::RemoteFetcher::FetchError)
No route to host - connect(2) (Errno::EHOSTUNREACH)
getting size of
the reason , i couldnt figure out .

Now i downloaded the gem from “
and again tried to install the gem moving to that directory. The same is
thrownup this time…what could be the obvious error? any
help/suggestions greatly appreciated…