+1 on buying a bike computer
+1 on riding more hills

I actually find that I can get up hills easier if I increase my cadence going into the hill. I cruise at around 90 rpm normally, but when I want to get up a hill, I kick it up to around 100. I discovered this completely by accident. One day I was riding home and I found myself actually increasing speed on a hill that normally kicked my butt. I looked down at the computer and saw that my cadence was way up. Practice comfirmed that this works for me (though it may not work for everyone).

As for improvement, check out the tips on this link:

http://bikenhike.com/page.cfm?pageid=22&tipid=65

My normal commute has the two biggest hills stacked right on top of each other with a dip in between, so it is perfect for building climbing strength. That reminds me of one other thing, if you've got a dip in front of a hill, don't go all out trying to build up speed to take the hill. It wears out your legs before you start. If you've got a situation like this, spin gently down the incline and be ready to work on the hill.