If you want a plan you are either going to have to:
- Find a coach
- Make your own
If you are competing then the first option is a must. You are going to have to include cycles of periodisation be it macro and/or micro cycles. This is not as easy as it might sound as the load varies continuously over a long period of time. You also have to take into account peaking just before the race and not be "blown out". The weights regimen needs to be done to perfection, assuming you are going to lift twice a week, the setup has to be that you don't gain to much strength with muscles becomming "slower as they get stronger" nor that you can muscle mass due to hypertrophy. None of these things you will get for free.
On the other hand if you are trainng for it just to "take part" then I would focus on running and swiming. The bike ride is pretty simple in relation to other two and the fitness for it should come naturally. Depending on how much you are going to be training for the triathlon a 2:2:1 ratio of R/S/B would work nicely. Recently there was a podcast where the USA Triathlon team was interviewed
http://www.competitorradio.com/details.php?show=303. You can get an idea of the ratios of training and also how much strength IS NOT A FACTOR!