if you have the budget, even a pair of good full range floorstandings can blow away a set of surround pc speakers... its largely going to depend on your available space too, such as, if everything is too close proximity, you wont get the full sound and dispersion... and it may not be worth investing in some though 'if' the source media is mainly just poor quality mp3s and such. but, assuming the source media is great quality (and you have the available space and budget), you really wouldnt want to go with anything less than a sound set you can assemble individually even, speakers, components, interconnects, and all, basically a DIY HT set. the room also does play a fairly large part in how things sound too, as do where the speakers are positioned... too many soft surfaces will absorb the frequencies, dulling and deadening the sound, and too many hard surfaces, will cause more echo and reverb, more of a loud headache and distraction to say the least. so at the very least its good to have a balance when possible, mostly softer surfaces on the sides and below (carpets, padded placemats, and softer surfaces underneath, and sheets or something softer on the walls), and more reflective/harder/solid surfaces towards the back and ceiling, but not all one way or the other either. (some environments simply sound horrible, and others sound better, as was pointed out in another post), basically more of the difference between how a movie theatre is designed, speakers, seats, materials, and all, and how something with absolutely no real desirable room acoustics is.
if you have the money though ($200-300), a decent pair of floorstandings (~$100+, 8 ohms usually) and a surround receiver (~$100+, 5.1 minimum, also usually 8 ohms minimum per channel), would definetly be the way to go for any pc, IMO. and that way you can add bookshelves/satellites, a powered sub for additional bass (.1 LFE 'bass effect' channel for dvds mainly), and whatever else later on if you wanted.
personally, ive found that the crossover frequency for surround satellite/sub setups usually isnt the smoothest... the satellites have all the higher frequencies, and then the powered sub comes in booming from an off angle more or less (its omnidirectional, so placement doesnt matter too much, but closer to a corner is usually the best way to maximize the bass output, and vice versa). but, again, if you have the space and money, floorstandings can do a great job of taking over the whole audible frequency range by themselves, especially with more drivers usually, covering different frequency ranges (usually 3, 4, 5 or even more drivers in a single speaker, usually called 2-way, 3-way, 4-way, etc, by the amount of crossover links it has), much smoother. you can usually hear them easier without having to turn the volume up by much (excursion?), i guess the speaker cabinet usually does a pretty good job of projecting the sound from the drivers, and amplifying the bass from a passive radiator/bass chamber/bass port, etc, and filling up the room as a result, and as a whole, but not just because the volume is louder really (thats probably not an accurate description, but im sure most people probably know what i mean)
sound clarity and distortion is also something to consider, SnR, THD, etc... i guess those would be largely dependant on the actual drivers, beyond that though, not too sure... the listed wattages though dont really matter too much, you can get a set that says it offers a lot, but more than likely youll just end up with a lot of loud unclear sound when you turn the volume up (theres not much speaker excursion when it comes to satellites usually, typically due to their smaller sized drivers/mainly higher frequencies, and lighter weight/flimsier construction, and the sound is usually fairly narrow as a result, meaning you absolutely have to have them directed at you to hear things well, i guess theyre pretty much limited to on axis dispersion then, its called i think, and listening from more off to the side isnt really an option if youre wanting clarity too, which is off axis dispersion), so turning up the volume cant really compensate for that, all that would do is make things louder. however, if the satellites are heavy (at least a few pounds or so each), most likely theyll be able to project sound pretty well without additional volume, or higher wattages.