I find security suits to be a waste of memory and resources overall. On my machine i have two things: AVG Free antivirus and ZoneAlarm firewall, also free. The antivirus covers most of the things you might want: active file scanning, e-mails scanning, spyware protection etc. ZoneAlarm ensures...
This might be a longshot, but if you don't require a lot of space, why not just get a flash drive? You can run the software and have some portable data storage.