you should be able to pick up a set of media speakers to just plug in, otherwise, you can get usb soundcards that have jack plug sockets in,
the speakers on the laptop are probably quite good, but not for playing loud music or films etc,
ive got a set of dell speakers on my pc, they are loud and clear till a very high volume, i do however have a big box thing for the bass, which if you need to be able to carry them around in a laptop bag, wouldnt fit..
but, coincider buying something like the A525 in this list on ebay (i think you'll have to copy and paste the link) if you want quality then pick a name you know of, dont just buy any old crap, you might be able to get some really loud speakers for a �10er but they probably wont sound too good,
http://search.ebay.co.uk/search/search.dll?cgi url=http%3A%2F%2Fcgi.ebay.co.uk%2Fws%2F&fkr=1& from=R8&satitle=dell+speakers&category0=