I typically use marks a and e to hold the start and end of a range (go to the line and hit m{CHAR} to put a mark in {CHAR}), then I can operate on that range with s/// like so, eg for pound commmenting:

:'a,'e s/^/# /

You can also use line numbers, 1 to $ ($ is the last line), a solitary % for everyline, and . or blank for the current line. To illustrate the "blank", these two commands do the same thing:

:,$ s/^/# /
:.,$ s/^/# /

Your idea to match on the end of the line is good, but won't work as you expect. The ^ meta character matches the begining of the line, the $ meta character matches the end of the line. (Vim is smart about guessing when you want to match $ exactly instead of end of line, regular vi is less smart.)

To replace the new lines themselves, first place anything you want at the end/start of the lines with a regular "s///" then use the ":'a,'e join!" to remove the newlines. (Regular join, ie no exclamation mark, will join lines with whitespace styled for English text, eg one space normally, but two spaces after a period.)

You can get very fancy with the "addresses" for the line range of any ":". To use an apache conf example:

:?^NameVirtualHost?+1,/^<\/VirtualHost>/ s/^/# /

This states search backwards for a line that starts with "NameVirtualHost", then start on the line after it (+1), and search forwards for the end of a virtual host (</VirtualHost> at the start of a line), and on that range put "# " at the start of every line. Essentially, comment out the first virtual host entry when I am on some line past the NameVirtualHost declaration.

That's a bit ugly in it's results though, since I always have a blank line after the NameVirtualHost, and it will be "commented out". So here is a more complicated one that won't comment out blank lines:

:?^NameVirtualHost?+1,/^<\/VirtualHost>/ g/[^ ]/ s/^/# /

The global (g/regexp/) in there says on the lines in this range operate if the character class of anything except space (and newline) matches. "g/re/p" where p is print, is the origin of the "grep" command. Another way to do roughly the same thing is:

:?^NameVirtualHost?+1,/^<\/VirtualHost>/ v/^$/ s/^/# /

The "v" is just like global, except the substition will only happen on lines that don't match. In this case, the regexp matches lines that begin and end at the same spot, ie blank, so the s/// runs on the non-blank lines. You'll see a difference if you have spaces on your blank lines though.