Thinking of getting my parents a ZeusGuard
 

http://www.zeusgard.com/

They only have one computer. I was gonna show them how to boot into this and use it only for checking their bank account online.

You can probably achieve this by yourself with a USB stick with Ubuntu live on it and a few extras added.

But for the price (now that I checked it) you might want to save yourself the hassle and buy it :)

Pretty good product if it works well.

Yea, I ordered one off Amazon. Since the USB is read only, Not sure if updates will be possible if there are problems with the browser.

I have no idea what OS or browser is being used. It probably is a Linux distro on a USB stick.

Ya know an evil guy could buy a USB stick loaded with a malware infected linux distro and slap a zeusguard sticker on it.

Brings us back to option one, buy a 8Go USB stick, install Ubuntu live on it with persistent space to allow updates.
Add a firewall of some kind.
A virtual keyboard (random positions) for the passcode

That's as safe as you are going to be.

Yea, That is the best option.