how to limit my bandwidth to test mywebsite / applications
Solution 1:
I'm going to assume you are on Windows XP or Vista since if it were something more interesting (linux or Mac) you would have said so.
I haven't tried it myself, but this may do what you need and it is free: Bandwidth Shaper XP
Solution 2:
Not sure about an app but you could try to use functions of your router to limit bandwidth, especially with some of the Linksys models like WRT54G that can be loaded with 3rd party firmware for extra features like that. Maybe use QoS somehow?