Hmm, less than a GB of RAM. Have you tried Microsoft Security Essentials w/ ZA Firewall. I think it's a great combo.
Otherwise, you could try something different like Emsisoft Mamutu or Comodo Firewall, a secure browser like Comodo Dragon w/ NoScript, and Sandboxie to open suspicious files. Disable autorun/immunize your USB. Also, there is Zemana AntiLogger. You can forego the realtime AV and do with an on-demand scanner like MBAM, Hitman Pro, VirusTotal Uploader.
The latest version of SpywareBlaster supports Chrome as well, so you can look into that.
You can try various combinations of the above to see what suits your need. With 894 MB of RAM, I cannot imagine using a security suite or even a realtime antivirus. This is how I survive without one: http://malwaretips.com/Thread-Why-I-don-t-feel-the-need-to-use-realtime-AV but again, it all depends on how comfortable you are and your internet browsing habits.
Another idea is that you can run Ubuntu or Linux Mint.