You can do that all in one loop.. you only need a counter, to determine where you are in the loop..
Example snippet of code:
// If the query has posts
if( have_posts() ) :
// Create a counter variable
$counter = 0;
// While there are posts, aka The Loop
while( have_posts() ) : the_post();
// Increment the counter in each iteration of a post, by +1
$counter++;
// other regular loop stuff
// If the counter is 1 or 5, then show full content
if( $counter == 1 || $counter == 5 ) {
the_content();
}
// Else show an excerpt
else {
the_excerpt();
}
// End loop
endwhile;
// End if have posts
endif;
Alternatively you can check some of the previous threads asking similar questions.
http://wordpress.org/search/first+post+full+second+excerpt?forums=1
The code involved is usually the same, so don't worry too much about the search terms i used above.