As you will soon find out in a notebook, you need to buy what you need up front (outside of memory but you only have 2 slots you you have to buy 1 memory stick upfront if you want to add your own RAM later to the 2nd slot -- many desktops have 4 RAM slots).
Notebook motherboards are proprietary (while many desktops have relatively generic motherboards and you can even replace motherboards in many cases on a desktop -- not on a notebook).
So, you need to get a notebook with a dedicated video card if you want one upfront while on a desktop you can easily add one with an open expansion slot.
LCD monitors are an array of fixed pixels (which is why you have only 1 native resolution unlike adjustable resolution on CRT monitors which is why many gamers still have huge 21" CRT's. If you have dead pixels you normally can't do anything about that.
A CRT uses an engine to shine the display through an invar shadow mask or other technologies but LCD's are fixed independent pixels so if one is bad it is bad and that is it.
For cpus you are limited to what the manufacturer motherboard and notebook bios supports only. So, if you have a Centrino Pentium M system you could upgrde from a Pentium M 1.4 to a Pentium M 2.0 but not to something else. However, depending on the age of your notebook you might need a bios update to accomodate a new processor. Also, for instance, early Centrinos had PC2100 memory and then PC2700 memory and new models are faster than that. There were bios and chipset changes to achieve that (and now the Centrino bus speed has gone from 400mhz to 533mhz) so you can do nothing to upgrade that.
So, on a notebook, outside of RAM and hard drive or minipci card upgrades (and that can be limited by bios as well) get what you want upfront in order to last you for 2-3 years of productive use.
I've built and worked on many PCs but working with laptops is a new area for me. I own a Thinkpad T21 and I want to change the CPU. How do I even BEGIN to choose and buy the right CPU? Help!!!
Also, how do I fix dead pixels (I have a permanent straight green line going down the side of the side) on my LCD screen?

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