It is doable with 1gb RAM and using vim/commandline tools. However, eclipse provides a project wide perspective which is hard to duplicate in vim (vim power users may be as productive, if not more though). So in terms of memory 1, 2gb RAM will be fine. Testing on devices is always better than emulators.
One thing else though, a commandline build with multiple module dependency is non-trivial to setup and maintain. This is because Google has historically been modifying the build.xml file, breaking existing build scripts fairly regularly. So if you are well versed with build script internals and prepared to work on them you should be ok.
Debugging Android apps without Eclipse based breakpoint debugging support may be a significant issue too. Some bugs are caught in a lot lesser time with this. So plan accordingly if you don't want to use Eclipse.
Eclipse also provides very good JUnit/Robotium support for writing test cases, You won't get this with vim.
As I wrote down these points I think running Eclipse in 2gb notebook should be possible (just don't run other apps with doing development) and thus is recommended.
I have extensively used vim just not for Android development. You can also install vim plugin for eclipse if you prefer that.