^^Theoretically, they may, but not practically!
Look, what i meant was, the quality of amplifier built into subwoofer units actually set the difference. Look, u are going for a 5.1 speaker system. There are things u may want to consider like, set of frequencies and better satellites to reproduce them. Plus, the overall power of speakers are better judged by RMS ratings instead of PMPO! Creative, Logitech,Altec Lansing and Philips cover all the required warranty and after sale services in India. Plus, they are reputed. Look, a 5.1 speaker should have right set of Center and Surround speakers along with a LFE to create a theatrical effect in your living room. By that, the system will require proper power distribution to all speakers i.e. Front L/R, Surround L/R, Center/LFE!
Look, as Desii suggested those models, they are nice. Just add one more to list: Philips 5.1 MMS460. From my experience, this set excel while in Gaming than others in its category.
And regarding soundcard, if u cant go for X-Fi then go for Audigy 4. I heard, Audigy and SB series have driver issues in Vista, though. So, choose accordingly.