The IP Address on the iPod Touch can be found in the Settings app. Open that and then select wireless or WiFi. In there it will find the list of networks in range. Ideally, your WiFi network should be in that list. If you tap the blue arrow next to the item in the list, it will show some more properties for that network.
This will be where you can find your IP address.
If you have a wireless router that uses DHCP for its addressing, you may have to check that the address is the same or check what it is, each time you try to use WinSCP. Alternately, you can set up your WiFi router to give you the same IP address each time. But you'll need to ask at another forum for tips on how to go about that...
