Created attachment 121297 [details]
The VIM plugin

This is the plugin. It has one small bug which I couldn't figure out. When you press F7 in insert mode at the beginning of a line, the cursor will be moved to the right. Pressing F7 in all other columns works though. I think that's a minor issue that can be fixed later.

Created attachment 121348 [details]
Improved, configurable version of the plugin

This is an improved version of the plugin. The plugin is more configurable in .vimrc now.

To enable devhelp search:
  let g:devhelpSearch=1

To enable devhelp assistant:
  let g:devhelpAssistant=1

To change the update delay (e.g. to 150ms):  
  set updatetime=150

To change the search key (e.g. to F5):
  let g:devhelpSearchKey = '<F5>'

To change the length (e.g. to 5 characters) before a word becomes relevant:
  let g:devhelpWordLength = 5

Thanks! Committed to trunk.