Which best bang for my buck for a PC 5.1 Surround System ?

I need a very good quality 5.1 surround system for my PC, but for a reasonable price.
I am hesitating between 3 models :
- Creative MegaWorks THX 550
- Logitech THX Z5500
- Altec Lansing VS3151R
Which one is the best, from your advice ?
Otherwise which other system would you suggest to me ?
Thanks.

Thanks for comment.
You are perfectly rigth that a full 5.1 hifi system is much better than a PC 5.1 system.
But, in that case, I can tell you that there is much better that a Sony, and some Bose, out there, and still for a reasonable price !
After many researches, I have come to the conclusion that the best bang for your money in 5.1 hifi system would be :
- A/V Tuner Hifi 5.1 Amplifier/Receiver : NAD T753
- 5.1 Hifi Speakers : JMLab Focal Chorus
Because, between you and me, japanese stuff for receiver really sucks, and Bose is out of the question if you are a really good music lover !...
Anyway, I must repeat my question, because I would still like to know what is the best PC 5.1 system, for example, if I feel incomodated into investing in a full Hifi 5.1 system (receiver + speakers) :
So, which one is the best for the best price, could someone tell me more about that :
- The THX Creative mentionned above ?
- The THX Logitech mentionned above ?
- The Altec Lansing mentionned above ?
- Any other suggestion, folks, thanks.
Thanks.

GET THE LOGITECH THX Z5500,it is awesome!! ..My uncle is really into stuff like this and he bought the Logitech THX Z5500 and loves it, my brother already owns a $2000 sytem and once he heard these at my uncles house he also bought it....they both say it was definitly worth the money!