|I think a company Shiva made a dual modem deal for POTS dial up. Most isp's don't offer shiva at their end anymore.|
If you mean two cable modems or two dsl modems then that is a different deal.
You'd have to run a virtual machine that was setup to do that or get a dedicated switch that is made for two or more internet connections.
"Best Practices", Event viewer, host file, perfmon, antivirus, anti-spyware, Live CD's, backups, are in my top 10