Weight lifting and running schedule?

Hey all,
I've recently been more involved with running.  I try to run 4x a week.  Tues, Thurs, Sat & Sun. 
I'd also still like to workout using weights.  How would you add weight training in? I don't necessarily have to lift weights every time I run, but don't want to add a 5th workout day.

I only run for about 30-45 minutes at a time.  3x are on a treadmill, 1x normally in a park.

What would you do?

I have a very similar schedule.

I would either space it out based on the day...so run in the morning and weight train in the evening....OR alternate days...so do weight training on your off days. It is important to have break days. I find that I go crazy on the days I don't run, so I go to the gym and lift weights. Other times, I run and lift weights on the SAME day to get it over with, so to speak.

Any other questions let me know

Thanks for the info.

There have been studies that say that only 20 minutes of resistance training immediately prior to half an hour or more of cardio will increase the 'yield' of BOTH workouts exponentially.

I intend to test this theory myself as the weather begins to cool ... Haven't been doing nearly as much running as I should be because the heat and humidity in my location, coupled with my work schedule have precluded decent outdoor running.

Good luck to you!