You can combine multiple internet connections using the gateways tab of any service in WinGate that has one. The gateways tab let's you control how that service uses the gateways it has available to it.
Set the connection scheme to "Use gateways in rotation" and add your two dial up modems to the list of gateways. This will make the service rotate all outbound connections around the listed gateways.
I have included an example screen shot. I only have one network adaptor on this computer, so I just added it twice.

- gatewayrotation.GIF (21.12 KiB) Viewed 3224 times