What weight training to add???

I'm looking at adding a weights element to my training to build some muscle/power but am wondering how to incorporate it into my schedule? I've lost 21lbs of fat recently and am now 172 lbs/16% BF and want to add some lean muscle while losing those last few pounds of fat.

I'm currently do a cycle of swim/bike/run/rest each day and am beginning to get used to that much activity and thinking about how best to add weights. I looked at Ron's prog on the site but this is too much for me right now as I dont have much time (perhaps 2 sessions per week) and probably would end up well overtrained, so am looking to a design a focused programme for max benefit and have a couple of questions:

1. Which muscles/groups will give the best returns on my time when the focus is sprint tri's?

2. Which activity days should I add them in? Can it be done on 'rest' days or should these be total rest?

3. My legs feel well worked from my current rides/runs so is adding squats etc going to be overtraining them?

4. I have a home Total Gym that replicates most exercises pretty well (& is v convenient) and wondered what exercises and approach people have the most success with eg heavy weight/low reps or higher reps/low weight?

I know this is probably a personal thing but would value people's input.

Thanks BP