sorry took so long to respond...
but definetly. though most receivers will come with at least a few different connections, which given what youre looking for, is almost guaranteed to be overkill anyhow, unless you find other things you may want to connect later on too, such as you may want to later dedicate it to being strictly a home theatre setup, maybe in a living room for example when they outlive the life of your pc, which is something that you really cant do well at all with pc speakers. but that aside, heres some ideas for the receiver and speakers:
Sony 5.1 A/V Receiver - $118 (i added this afterwards, it comes with HDMI support too, coincidentally)
http://www.amazon.com/Sony-STR-DG510-Home-Theater-Receiver/dp/B000OG6I8S/ref=sr_1_1/104-0650996-8529545?ie=UTF8&s=electronics&qid=1192337087&sr=1-1
Sony 6.1 A/V Receiver - $140
http://www.amazon.com/Sony-STR-DG500-Channel-Theater-Receiver/dp/B000ETYO7C/ref=sr_1_8/104-0650996-8529545?ie=UTF8&s=electronics&qid=1192331750&sr=1-8
Sony Center Channel - $88
http://www.amazon.com/Sony-SSC-N5000-Center-Channel-Speaker/dp/B000OGA81Q/ref=pd_bbs_sr_1/104-0650996-8529545?ie=UTF8&s=electronics&qid=1192331074&sr=1-1
Sony Center Channel and Satellite Pair - $55
http://www.amazon.com/Sony-SSC-R3000-Channel-Speaker-Package/dp/B000OG88NQ/ref=sr_1_4/104-0650996-8529545?ie=UTF8&s=electronics&qid=1192331074&sr=1-4
Sony Bookshelves - $49 per pair
http://www.amazon.com/Sony-SSB-1000-Book-Shelf-Speakers/dp/B000OG88KY/ref=pd_rhf_p_t_2/104-0650996-8529545
Sony Bookshelves - $85 per pair
http://www.amazon.com/Sony-SSB-3000-Shelf-Speakers-Woofer/dp/B000OG6I6A/ref=pd_bbs_2/104-0650996-8529545?ie=UTF8&s=electronics&qid=1192331074&sr=1-2
Sony Powered Subwoofer - $67
http://www.amazon.com/Sony-SA-W2500-Performance-Line-Subwoofer/dp/B000OL3QTW/ref=sr_1_2/104-0650996-8529545?ie=UTF8&s=electronics&qid=1192330532&sr=1-2
Sony Powered Subwoofer - $120
http://www.amazon.com/Sony-SA-W3000-Performance-Line-Subwoofer/dp/B000OL22T2/ref=sr_1_3/104-0650996-8529545?ie=UTF8&s=electronics&qid=1192335500&sr=1-3
so, depending on how many and which model speakers you might get, youll stay under your $400 budget, possibly by a lot (the cheapest 5.1 speaker/receiver combination came out to $289). if you were to get a surround amp and just a pair of floorstandings ($233 cheapest combination from the list), it will definetly sound better than the $289 5.1 combo, but it offers no surround then either, as its only 2 speakers, you can always add more speakers though, of coarse
and if you later wanted to, you could add a surround back speaker too, since the 6.1 receiver will allow for 6.1 channel dd-ex and dts-es decoding. it might also allow for splitting the single surround back channel into 2 seperate surround back channels, as some 6.1 receivers will allow that, effectively creating 7.1 surround. and so if you later wanted to purchase floorstanding speakers for use as the front speakers, instead of purchasing even more bookshelves, then heres some examples:
Sony 3-way Floorstanding Speakers - $115 per pair
http://www.amazon.com/Sony-SS-MF650H-3-Way-Floorstanding-Speakers/dp/B00029U12Q
Sony 4-way Floorstanding Speakers - $175 per pair
http://www.amazon.com/Sony-SSF-6000-Floor-Standing-Speaker/dp/B000OG4E20/ref=pd_bbs_3/104-0650996-8529545?ie=UTF8&s=electronics&qid=1192331074&sr=1-3
(you could also purchase 1 front center channel, 1 floorstanding pair for the fronts, 1 bookshelf pair for the side surrounds, and 1-2 other bookshelf speakers for the back surround(s), and maybe 1 powered subwoofer for more additional bass that you can position elsewhere, such as closer to where a person might be sitting; floorstandings effectively replace the need for a seperate sub, but a seperate sub can be helpful as well, if you need additional low frequencies)
as far as 5.1 satellite and sub setups, heres a set that was given to me as a gift at christmas, it was purchased for $200 in 2003 at best buy, this online retailer is selling them for $350 though, probably because theyre no longer available. they had sold for as much as $800 at some places, but i really cant imagine anyone having paid that much for them
Sony 5.1 Satellites and Sub
http://www.amazon.com/Sony-SA-VE445H-5-1-Channel-Surround-Speaker/dp/B000095R9P/ref=sr_1_1/104-0650996-8529545?ie=UTF8&s=electronics&qid=1192333205&sr=1-1
so a pair of the above listed 3-way floorstandings 2 years later really helped to smooth out the remaining range that the satellites and sub were lacking by themselves, it was a significant improvement, to say the least.
but, all of the above listed speakers are matched fairly well as far as specs and such, being as how theyre all from the same relative range of models. frequency range, materials used, and all that, meaning they should all sound pretty similar to one another... i guess even colors are matched for that matter too, from an aesthetic POV.