Can someone tell me what's the best processor for a laptop ? amd, intel, celron, how do the speeds correspond to reality ?

What do you plan on using it for? An AMD Sempron or Intel Celeron will work fine for "normal" use. Get an AMD Athlon64 or Intel P4 if you need more power. Intel's Centrino package is based on the Pentium-M CPU which is supposed to powerful, yet runs very cool & low power consumer (longer battery life). AMD has recently countered with the Turion64 package which has similar characteristics, but it's a 64-bit CPU

For the most part, laptops/notebooks are not good for gaming...if that's your intention plan on spending $1500-2000+ for one with decent video & dedicated RAM. Integrated graphics with shared RAM won't cut it...

ASUS A7N8X-X
Athlon XP 1800+
8.5 x 200MHz
1024MB PC3200 2.5-3-3-7
Asus A9550GE/TD 128MB
WinME/WinXP Pro SP2

Get the AMD Turion 64bit, it's good if not great on battery life plus it's 64bit. As of now Intel makes no 64bit laptop processors. So if you buy an intel based laptop now you won't be able to jump onboard the 64bit wagon later.

Intel will go 64bit by early next year on both high and low end laptop models and the Sempron laptop model will also go to 64bit as well by late or early next year from what I have been reading.

So yeah at this point and time you want to go 64bit considering 32bit will all but die out in 2007 when both companies stop making 32bit chips altogether.