Ubuntu Variant / Linux Distros which uses least system resources (RAM, CPU)?

view story

http://askubuntu.com – I have a netbook (an older Asus EEEPC 1005HA) which I want to get rid of Windoze on (I like Windows, but I don't think it works well in a netbook environment). Basically, my question is which Ubuntu variant will use the least RAM and CPU running idle, and/or the same question except when running Firefox and Libreoffice Writer, say. I am also open to suggestions of non-Ubuntu Linux distros, but since this is AskUbuntu I thought the first question would be more appropriate. I have a disk drive which I can attach to the netbook, so it doesn't have to be a Ubuntu Variant / Linux Distro which so (HowTos)