Upgrading

No, no, yes, and no.

 

To elaborate on what edblor mentioned,

Buying the low end Pro and upgrading the hard drive will technically void the applecare warranty if the model you are purchasing is not a unibody model. However, if you are getting a Unibody then upgrading the HDD and RAM should be fine. Just make sure that if you do upgrade the RAM that you keep track of all 8 of the screws for the rest of the underside of the computer.
You should be just fine under applecare. (though to be very honest, Apple care is really only good for manufacturer and Apple authorized repair defects)

If you buy a new HDD from newegg, you will have to format it. every new hard drive I've ever bought has come with either no file system or one of the 2 windows filesystems, Fat32 or NTFS, on it. Mac OS X cannot boot from either of them, so you will have to reformat to HFS+ journaled [case-sensitive] (case-sensitivity is optional). Its extremely easy since the install disc comes with the Disc Utility program on it so you can load up the correct filesystem from within the install disc.

Fianlly, no there really isn't a difference in the max allowable RAM upgrades. Apple will tell you that the max is 4GB, which is true if you wish to make use of Dual channel capabilities of your RAM. You can go up to 6GB, but you lose the Dual channel capabilities.

 

No, upgrading your RAM and HDD does not void your warranty. However, if you ever have trouble with it put the original RAM and HDD back into your laptop. Otherwise Apple will just blame your new hardware for your problems.

 

if you didn't break anything, then the warranty is still effective.