Currently Being ModeratedFeb 11, 2013 5:58 AM (in response to akwandaltw)
the cheapest way would be to buy a mini jack to xlr audio lead. you dont need an interface.
the mini jack takes the output from your computer and the xlrs plug into the speakers.
depending on where you are in the world, try studiospares.
using an interface will give you better quality, but not that it matters for the vast majority of situations.