I'm only on Week 2 of the C25K, so I'm not dealing with any soreness yet. I'm actually fighting to keep myself from jogging on the off days, but I've kept up my normal hour of walking on those days.
I'd really like to alternate the two of them, I certainly don't think it would hurt anything. I was planning to wait until after this week to start the 30DS. I tried Day 1 earlier in the week, but TOM is here and those jumping jacks were killing me. It felt like a bad mammogram times a thousand.
What week of the C25K are you on?
1000 miles in 2010 - 7/1000