I agree with Mr. Finley on Toshiba. As to an "interface", you don't need one. You're not recording, just using the laptop for playback. You don't need a recording interface for that - it's overkill, and you won't hear the difference through a PA. The integral sound module in the laptop will be 16 bit/44100 Hz/CD quality, which is sufficient. I run audio and MIDI on a $400 Toshiba Satellite laptop into two different PA's with zero problems.

You will have to upgrade your PC to Mixer connection, though. These are cheap, and give you two balanced lines to your mixer, and it's stereo/mono switchable:

http://www.musiciansfriend.com/pro-audio/peavey-usb-p-usb-di-format-converter


Keep it simple. The Peavey is plug and play, and transformer-isolated to eliminate ground loops.