You do not need a broadband connection to use this.
However, if you're going to use it primarily to share files between PCs, you should be aware of the relatively slow speed of 802.11b. B is great for Internet surfing -- as someone noticed, you're not likely to do better than that on your regular "wired" connection. However, for moving big files between computers, you're going to notice a significant speed difference between 802.11b and 802.11g or 802.11a. (Neither will be anywhere near as fast as a "wired" connection.)_
If you're looking to invest in a route and think you will get broadband soon, I think this is a smart investment -- so long as you realize the real benefits are in the Net connection, not in sharing files between computers on the network.