To be honest, no. You don't mention the OS, I assume you're talking XP but even so it's still a no I'm afraid. Even if you didn't install any of the extra features such as device, data control you'd still have a hard time. If the machine was dedicated to just running Sophos it might be ok but I assume this machine is to be used for something more than that? :)
I would suggest 512 would be a minimum for the machine to be usable.
You could still protect the machine to some degree with scheduled scans by running SAV32CLI maybe once a day when not being used but this is all I would recommend. You could try it but I have a strong suspicion the machine will be very slow especially to boot.
