Hi Lawrence,
You can setup a site to site IPsec tunnel between your 800 (IOS router) and pix. I have the setup for one of my customer.
You need to make sure that 800 router with K9 bundel image example: c870-advipservicesk9-mz.124-15.T1.bin
Now you can create a vpn tunnel for temporary or for permanent.
Please rate the helpfull posts.
Regards,
Naidu.