Different speaker types in one home theater system?

Before I ask any questions, I just want to mention that I'm not, in any way, knowledgeable at this at all. I've been trying to setup my home theater system by reading forums on the web. Here are my questions:
1) I've a SONY home theater in a box. However, I would like to buy 2 different front speakers, like from YAMAHA. If I do that and unplug 2 front speakers of SONY and connect that wiring to the YAMAHA speakers, will that be alright?
2) I also have PC where I store DVD's. The sound card is Creative Sound Blaster and has one line output. But in the SONY receiver, it expects two line in. Is just buying a splitter kinda cable will solve my problem with hooking PC to receiver for the sound to come from the receiver. The video part was easy cause I just hooked up the s-video to s-video in TV.
3) The receiver does not have any component plugs. Buy my HDTV has component plugins. How can I make the sound come from receiver if i'm using component connection from DVD to TV.
Thank you for all your help in advance.

You can mix speakers, however only to a certain extent. Generally you want to match the fronts togehter and the backs together, although some on this forum will argue against even that.

Yes you can buy a splitter and split the signal. It will not sound very good, but then again your system isn't that sensitive (I didn't mean any disrespect, but HTIB's are only so good). To get better sound out of your PC stuff you may want to invest in a better sound card with at least a left and right outlet.

I thought I was investing on a better sound card by buying "Sound Blaster Audigy 2 ZS Gamer Edition" rather than using the built in sound from the motherboard.. I guess I need to find another sound card w/ left/right option... Thanks for the help !! I really appreciate it.