I don't know of any laptop that has more than 2 slots, and I don't know of any laptop that has less than 2. In short, they all have 2.
If I were to buy a new laptop with less than 2GB, I'd get the smallest amount possible and buy my own $75 2 X 1GB kit, or maybe a 2 X 2GB kit if I was planning to game a lot and multi-multitask.
I f you buy a system with 1GB, it will be 2 X 512MB sticks. If you buy 512MB, it will be 1 X 512MB stick (most of the time). If you get less to start with, you're wasting less when you take it out. No matter what you buy, you'll be taking it all out to upgrade.
Unless you buy it with 512MB and add a single 1GB stick.
You get the idea.