Gigneil - a CPU is the central processing unit (aka the processor). TFT is the type of LCD
(a few years back the lower end notebooks had STN
or DSTN type LCD
displays) display - so these two are not really connected.
Now to the questions...
Shared memory - nothing bad per se, but it's considerably slower than dedicated video memory (there the GPU is directly connected to the video memory; in the shared-memory model this communication goes via the CPU which puts more load on the CPU and also "slows down" access to your RAM - because the memory controller now also has to deal with memory accesses by your GPU); okay 2D
speeds, very poor 3D - don't expect to play new games (or at least don't expect high fps). Also answered previously - it depends on the chipset whether you can select how much of your RAM you want to allocate as the video memory (so if you have 512 MB
and allocate 32 MB
as the video memory, your operating system will have access to 480 MB
Memory upgrades. As answered previously, on the current generation of notebooks you'll have 2 available slots with one already taken (occasionally both of them are already taken when delivered, so check this before you buy - or just remove one memory stick when upgrading).
I'm not sure about the warranty conditions, but I would presume a memory upgrade would not void your warranty - but do check if you want to be on the safe side.
You need to have at least PC2100, but PC3200 will also work; so just buy the ones that are cheapest
Yes, your CPU can typically be upgraded - but buying a mobile CPU is typically too expensive (there are exemptions though - for example the mobile Athlon XP
processors - which are in reality real Athlon XP
processors anyway (but they work on lower voltage due to the quality of the core)); so upgrading the CPU doesn't usually pay off.