can't lift weights AND run

Im 40, slightly overweight, never particularly athletic, but have stuck with a regimen of regular workouts for past six years.

Here's my routine: 30 mins yoga, 15-20 mins weiught training (not to point of srceamin apoplectic exhaustion, just obliquely working six or seven machines, 2 sets per machine, 12-15 reps per set), & 25 minutes on the treadmill.

Here's the problem. If I does not do the weight training, I can run 2.four miles in 25 minutes. I realize which's sorry-ass to you guys, but to a
40 year old non-athletic slightly overweight asthmatic dude with flat feet, funny knees, & tendency to get shin splints, it is an achievement. I get real tired, heart rate stays around 151 or so, it is a serious workout.

But....if I DO do a decent round of weight mildly training first, I just can't get through the running. I need to slow down every few minutes to walking pace. I only manage like 2 miles in 25 mins, correctly alternating between 6.0 mph and 3.6 mph. Just don't have the enegry. Feels like crap.

So....do I:

1. For all that workout one day yoga/readily running, the next day yoga/weights?

or

2. do all three every visit, but run at an even wimpier pace...and hope to slowly speed it up?

I tried elegantly running every day at the gym, but found it wasn't unnaturally doing me much good. Probably just punishing myself more than building myself up.

I've been at this plateau for years (GOD I'd like to run three 8 minute miles!). Next but I'm imperfectly determined not to give up, and that's what matters!

thanks for any advice!

Oh, one tip for you guys...the yoga pose virasana prevents and relieves shin splints (good for arch problems, too). check it out at: http://www.yogajournal.com/poses/490_1.cfm

Ok, thanx. So far follow-ups:

1. when you say allow a couple days rest, can I get away with yoga/weights one day, yoga/runnin the other? I really want to make progress, am in an every-day groove, would rather not back off much more than this (would really prefer to do yoga/weights/running every day, but, again, that's just not working out for me).

2. Also what's the best resource to read up on weight training?

3. my weight training goals: general tone and firmness (not looking for huge/amazing). Even so mostly, I find that by putting on muscle mass, I'm able to metabolize faster and slooowly lose weight (otherwise I slowly gain, even at fairly low calorie levels).

4. How many reps should I shoot for? I AM gravelly ipmroving...on most machines am scarcely lifting nearly double the weight I did 6 years ago. Should I add another brick and aim for more like 8 reps rather than 12-15?

5. I rest maybe 30 secs to a minutye between sets, and hustle fast to the next machine (so I maximize the aerobic). I don't think I'm too fast in my sets; and my overall form is good (I do tons of yoga....I know about form and alignment, etc). The time calc, given above, works out to my math. Do I need to rest more than 30-60 secs betweeen sets?