I also had an atom Aspire One a few years ago, it was a single-core hyperthreaded one. You can try the following things to speed these sorts of machines up:
- Classic theme (no shiny stuff)
- Strict control of startup processes (MSConfig). iTunes, Adobe stuff, etc. are usual culprits
- Sensible antivirus (I like MS Security Essentials)
- More RAM (as much as possible)
- ReadyBoost SD cards
- SSDs obviously
More drastically, here are some different OS options:
- Windows POSReady 2009 (security-updated, fairly light version of XP)
- Windows Thin PC (light version of 7)
- Windows 8.1 update 1 (allegedly runs fine with 16gb storage / 1gb RAM)