1. As for me I use my old 256 Mb sticks as a decoration for my desk.
2. As for the buying of 4 gb I don't know. I would only go that much inless you have a 64 Bit OS. If you have a 32 bit then you will only be able to access about 3 to 3.2 gbs of ram out of the 4gb.
3. Why get so mush for your laptop when you can make a desktop with 3 times the power? For me 2gb in a laptop is enough because there isn't that many memory heavy things you do on a laptop.
4. I would get a pair of 2 gb sticks because there tested together and set for each other.