Raid 5 question

Hey guys, I want to make a raid 5 storage server from an old P4 2GHz 512mb ddr computer that is sitting in my parts closet. I am planning to use 4 1.5TB hard drives and a rosewill 4 port pci sata II raid card. I have 1 Desktop and 2 Laptops on my network. The Desktop is going to be the computer acessing/storing files large files the most, while the other 2 Laptops maybe every once and a while will store a text document or a mp3. Is my old P4 going to be able to handle the load from running this raid 5 setup? and if this old P4 will be able to run my raid 5 setup ok, should I buy a 10/100/1000 ethernet card, because the onbaord card is only 10/100.