I know System 76 makes some nice Ubuntu machines (expensive though). https://www.system76.com/laptops/
Use Lubuntu and add more RAM (if possible).
For a little netbook like mine (Asus Eee PC 1005ha 1.8Ghz Atom 2 GB RAM) I think Lubuntu 13.04 is the best of breed, though Xubuntu and Kubuntu...
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