My original guess at what the OP wanted was a multimedia presentation PC - that requires nothing special.
Not all audio interfaces are PCI. You can get some high-end audio gear that connects via USB or FireWire.
If you want to get really serious about recording and engineering sound, I'd start by looking at some of the M Audio products: http://www.m-audio.com/index.php?do=products.family&ID=recording
Basic video editing doesn't require anything special either. High end video editing places serious demands on the machine, but that's a whole subject on its own
I guess we need the OP to be more specific about what is meant by "multimedia" before we can make any serious recommendations.