Athlon 64 are mainly for desktop PC. I don't even think Gateway or Dell have implemented Athlon 64 in any of their systems. They're all using the limited Pentium 4's.
You can put an Athlon in a Gateway or Dell PC... but you'd have to change the Motherboard generally; so to change a Notebook Processor to an Athlon you'd have to get a Notebook Motherboard for the Processor, and change it all. It may not be worth it
There are P4 mobiles Mr. Intel Lord K... I am AMD Zen, and even I knew that one.
Not to imply that I don't know about Intel either, I know just as much about them as AMD. I know PC hardware (definentally not software...) extremely well. Thus the Title ZEN.