If company policy for your location does not prohibit the use of the filesharing application, but they are concerned about bandwidth usage, you might consider making use of built-in rate-limiting capability (BearShare and other gnutella clients have this), as do others, to prevent network cloggage. Also, be responsible about how many different things you download (and allow others to upload) at once. Another thing you can do is use the program at times that others are not using the network (i.e. nighttime).
A lot also depends on what kind of media you are downloading. For example, edonkey is excellent for downloading large (100+MB) files due to it's segmented download ability, and doesn't have a lot of network overhead due to the semi-centralized supernode network architecture (you log into a server and search amongst your peers for files, but you can extend the search to other servers if needed). Gnutella clients are good for smaller mp3 files due to content availability. I haven't used the Morpheus/KaZaA network, so I can't speak for it.
-j