Hey Jmammo,
I recently joined just like you (ha, i am more recent!) and I too have been bitten by the rugby bug. If you're just looking to beef up your muscle mass (and maybe even a little fat mass) I think the best advice anyone can and will give you is to start eating up (healthily of course, with an emphasis on lean proteins, veggies, fruits, not too many simple carbs)! If you're not already eating a lot, I would suggest to up your calories until your weight starts reflecting the intake increase. Of course, at the same time, you should be hitting the gym and, I presume, working on speed drills to keep the fat from accumulating and to keep your speed up as your weight increases.
As far as an actual lifting routine, I am not really an experienced rugby player (yet) so I'm not sure which lifts are the most important, but it seems like the gold stars for rugby excellence come from having powerful, explosive bench presses, squats, deadlifts and perhaps the important body weight exercises (pushups/pullups, etc).
I've been lifting pretty seriously for the past 4 years, and I'll be honest, I have made a lot of mistakes in getting to know how my body works, and getting to know how I personally pack on mass and strength. So, of course, this may not work for you as our physiologies probably differ, but what has really worked well for me in terms of these things is to stick to relatively low reps and high weights for the basic lifts, and only doing at most 4 sets of each basic lift per exercise.
I know bodybuilders will tout the 15-20 set per bodypart workout (say, doing 5 sets of bench, 5 sets of incline bench, and 5 sets of decline bench), but I really feel like these workouts cannot be used all the time, as they produce too much muscle damage and fatigue to be used consistently. This is why, after years of using the "only one bodypart per workout theory", I have found the most success splitting my workouts into different exercises working different muscle groups.
For example, tomorrow I will perform 4 sets of bench, 4 pullup sets, and 4 bicep curls sets (I realize that biceps are hit pretty hard in both of the latter exercises, but I am seeing considerable mass gain in my biceps lately, so I'm not gonna jinx it!).
Thats my 2 cents. I'm by no means saying im an expert - I have a long way to goal to hit my goals of matching Andrew Sheridan's one rep max bench haha - but these have worked from my experience! Good luck, and hopefully this will all open up a healthy debate!