HVCC has 27 holes. The Flynn and Toomey nines are the origional 9's and the centennial was added as the third. The centennial nine is a great compliment to the other two as it is much harder yet maintains the same characteristics as the other two nines.
The interesting thing about these three nines is that they originally opened at the same time when Flynn completed the course back in 1928 (I believe). It's been noted that the nines increase in difficulty as you play them in A, B, C order (A="Toomey", B="Flynn", C="Centennial").
The C nine closed during the depression and was reconstructed back in 1998 give or take a year. It is the most difficult of the 3 as Matt mentioned above. The 3 put together make for a very fun 27 holes.
Although they have this perceived difficulty progression, I find the A and B nine to play to a similar difficulty with some very difficult holes on both nines. A sometimes more so for my particular game...the ball above my feet lie which is often found on the A nine is not my best friend.
HVCC has received much praise on this site and rightly so. It is one of the most fun golf courses you could ever hope to play when it is firm and fast (like usual). Very unique to the area if not all areas in the US.
Ok - enough of this love fest.