Laptop questions

hey all how good is a AMD Sempron 2800+ 1.6 Ghz compared to intel pentium 4 cpus. also is it easy to replace ram later on to a laptop? or do i have to send it in to the manufacturer? and the same goes for the hardrive because i might want to switch it later on. would i need to send it in somewhere? or can i do it safely at home? thanks in advance guys.