To answer a question you asked earlier...
Since you were able to setup the VPN from different wireless networks I don't think that NAT would be the problem. I wouldn't expect every open wireless network to have a routed subnet, so you had it working from a NAT environment.

I don't think you'll be able to download Cisco IOS upgrades from anywhere but Cisco (legally anyway). I'm sure I'll be told if I'm wrong about this

To upgrade the IOS on the router setup up a TFTP server on a pc you can reach from the router (you can download one from anywhere). Make sure you set up an ethernet connection to the router.
Log on to the router and go into enable mode. Type: copy TFTP Flash <enter>
The router will ask you some questions like filename and IP adres to copy from and will start copying the software from your TFTP server to the router. Reload en see it boot with the new version

Make sure the IOS version you use is supported by the router and obviosly backup the old IOS version and config before upgrading.

GL.

Morvai.