memory will help immensely, as long as your laptop will take it. you may only have two memory slots, and have both in use and end up needing two 512mb sticks... laptops suck for upgrades IMO. the processor would be a big problem because you may run into overheating issues that would not be as much of a factor on a desktop, possibly the same with a larger HDD. plus a laptop HDD upgrade can get expensive, plus will your mobo support it or even use it at the faster speed?
visit crucial.com and put in your laptop model, etc and it will give you what you need for a memory upgrade. you should be able to find the same ram for less elsewhere.