When designing a service portal there are two important things to keep in mind:
The differences between a TV screen and a computer monitor.
The TV is most often placed across a room whereas the monitor is close to the user. The monitor has a much higher resolution than the TV. Objects that are well suited for a web page may appear quite differently on a TV screen.
Performance differences between an IP-STB and a computer.
The resources in an IP-STB is not the same as in a computer. There are limitations regarding memory and processing power that will affect the performance of a portal.
While navigating on the TV screen, most users use a remote control with possibilities to navigate in four directions only (up, down, left and right). Try to design for a simple and straight-forward navigation that can be easily understood even by users not used to computers.
Remember also that not only are TV screens different from monitors, they also behave differently from one another. Therefore, test every step of developing a service portal on a variety of TV screens and not only on a monitor, to make sure that the colors displayed are the intended ones, that the information is clear and available and that the total perception of the service portal is satisfying.
In general, thin client systems have limited memory and processor resources. Make sure that you take this into consideration when designing the service portal. Small pages and fast feedback will greatly improve the user-perceived perfomance.