First Batch Problems

Hi everyone,
I've brewed my first two batches of beer, but I've now encountered the same problem with both during fermentation. These are the two recipes I used: http://www.brewsupply.com/HowTo/Recipes/playaporter.html and http://www.brewsupply.com/HowTo/Recipes/venicecrm.html.
OG for both was about 1.042. I brewed the porter first, and transfered it from the primary to secondary carboy when it was at about 1.020, which I now know was too soon, since fermentation didn't go anywhere from there. The beer definitely got too cold during fermentation so thats probably why it stalled, but then even after I transfered it to a fresh carboy and pitched more yeast, and kept temperature constant at a little over 70 (i'm pretty sure I kept it fairly constant, I used a water bath the second time around), the gravity is still stuck at 1.020. As for the cream ale, gravity is now stuck at about 1.020 as well, though I haven't pitched more yeast yet. Its possible, though I'm not sure, that the temperature in the cream ale may have dropped low as well. Should I just throw more yeast into both, or is there something else I might be doing wrong? I might not have let the yeast rehydrate properly on the porter the second time, or I might have mixed the yeast in too vigorously and let in too much oxygen.
I'm getting sort of frustrated, so any suggestions would be greatly appreciated. Thanks!

It's probable that you've simply exhausted your fermentable sugars. What brand is your extract?

I'm using Alexander's liquid malt extract, dark for the porter and pale fro the cream ale.

Did you aerate the wort before you pitched the yeast the first time? I read the brewing directions in the links you provided and didn't see anything about aerating.

Here is an article on attenuation in the Wiki that you might find helpful.

Don't give up, attenuation problems are pretty easy to fix.

I don't think I aerated the wort of either beer, other than when I poured it into a bucket to strain out all the hops and such. I did stir both after I had added the yeast. So what do you think the solution is? Add fresh yeast and monitor the temperature more closely?

If you poured the brew through a funnel into your primary that should be enough to aerate the brew. That is typically all I will do. If its a bigger brew I will shake it up real good also but its not a usual practice for me.