Why is my download speed really slow?

So one day I was downloading some music. It said it was going like 3 kilobytes per second. I have pretty fast internet and it only did this on one computer in the house. My connection for the computer is 5 bars out of 5 so I don't know why this is happening. If I download an app on my itouch, the download is finished in like 2 seconds. I have a Belkin wireless adapter plugged into my computer so I can get a wireless signal from the router. Also, when I download something, it goes really slow and sometimes freezes for like 10 seconds, then resumes. One last thing, the browsing speed and watching videos on youtube is really fast though.