45w vs 65w AC adapter

No, it isn't impossible. It's easy:

http://store.apple.com/us/product/M8943LL/A?fnode=MTY1NDEwMQ&mco=MTA4NDE3NzQ

Suit yourself. You've already guessed wrong once. I don't suppose you tried to invoke the warranty on your junk adapter?

A 45W adapter will take longer to charge your 15" machine, will get hotter while doing so, and won't supply enough power to run the machine and charge the battery simultaneously, at least not under a heavy load. It's a bad idea. Furthermore, the older Apple adapters aren't as good as the current one. The fact that your old one lasted five years indicates that you took good care of it, unlike most of the people complaining that their new Apple adapters fried after six weeks or the like. That simply doesn't happen to adapters that aren't abused. If you bought a new Apple adapter and took the same care of it that you took of your first one, it would easily outlast your computer's useful life.

The adapter below has been offered by many vendors under various brand names, and I've known several people who bought them. They're no better than Apple adapters, but they cost less:

http://eshop.macsales.com/item/Newer%20Technology/APLPBI65W/

OWC stands behind what it sells, so if you buy one and it fails, at least you'll have a warranty that means something.

Perhaps that was because they had a 12" powerbook 1ghz, and mine is more powerful?

Exactly. And they were talking about using an adapter with more capacity than the original, not less.

Check out the screen shot on the page for the one you link to...It says it's not charging.

That's because the battery was fully charged already. Note that the Full Charge Capacity and Remaining Capacity are the same, indicating that the battery is charged to 100%. Charging stops when the battery is fully charged, and does not resume (even if the AC adapter remains connected) until the battery's charge level falls below 95%. Charging the battery heats it, and this strategy allows the battery to cool off once it's fully charged and stay cool most of the time, even if the AC adapter is connected around the clock, day in and day out.

The adapter sold by OWC will charge your battery whenever it needs charging. So will Apple's adapter.