How can I secure files on an external hard drive?

Use Winsesame it is a powerfull encryption tool very easy to operate with a free version for small volume of data. Download the free version from http://www.aragonsoft.com/en/winsesame/
If you need to protect a large volume of data, the full version is not expensive. Do never use the password protection of zip and rar file. There is lot of tools to open those files without the password. Use a software specially developed for this purpose.
Peter

Peter
May 2010

Try this

http://www.keynesis.com/products/lockngo/

Mac
June 2009

You can use winzip or winrar and password protect the compressed file , its a really cheap program.

martin
May 2009