Nope, there not different in that sense.
Its just either 1 module of 512mb to use less space inside a PC, or two modules to equal the same memory but use more space.
Though there is a term called Dual Channel:
What this does, is if the motherboard and RAM supports it and you use two modules of RAM, it doubles the amount of memory that can be read at one time, and so theroretically almost doubles the speed of the RAM when used together.
i.e, I have 2x512mb chips to make 1GB because mine supports Dual Channel.
Though some Processors for example don't reward much from Dual Channel because of the speed they run at, and so sometimes, its best to get 1x of RAM, since it'd use less space for more upgrades later.
Though most PC's will get some reward from it, so its definietly a possibility if the Laptop supports this feature.