ASL can do tagged VLANs on a Ethernet interface. That should allow you to run up to 16 subnets out of the ASL box through one NIC. You will need ASL v5 to do this, since the Ethernet interface license limitation in ASL v4 also applies to VLANs.
The catch is, that you can not use the NIC for ordinary, baseband Ethernet at the same time. If you run tagged VLANs on it, that is all you can use it for.
The second catch is, that to distribute the tagged VLANs back into individual baseband Ethernets, you need an intelligent, managable switch connected to the ASL box, such as a Cisco 1900 (10BaseT), Cisco 2900 (100BaseTX), 3Com SSII 1100 (10BaseT) or 3Com SSII 3300 (100BaseTX). There are others that will do the trick, but those four models are the most common ones in the 2nd hand market. If you use eBay, the 3Com units are generally the cheapest ones to get your hands on. They also have a very nice built in web server, which makes configuring the VLANs a breeze.
....you could just add an additional IP address to a standard ethernet interface,which will give it the ability to talk to several different subnets, and not have to worry about the complexity of VLANS.
I'm not sure why you want to add two different subnets to one interface, but it is usually better from a secirty and performance viewpoint to seperate subnets with a router, and only have one subnet per interface.
