You're going to need two sounds cards, one will more than likely be external (plugged in via USB) as laptops don't have that much space inside for two sound cards. I think most of the computer guys use 1 external sound card with two outputs, it's a 2 in 1 deal. More experienced folks can name brands and prices for you.
For just music playback I'd recommend:
A mid range dual core processor at least 1.6Ghz; No Celeron or Athelon processors and 2 GB of RAM.
Hard drive space doesn't matter because you're going to be storing your music on an external drive. I'd get at least 120 GB though so you have room for your programs and about 200 songs should your externals go down for some reason.
3 External Hard Drives: Make two the largest that you can afford: 1 for your Music and 1 to back up your music. The third external should be roughly the size of your laptop's hard drive so you can place system images on it and in the event of a computer failure restore the system to a working state crazy fast.
As for brand, they're all pretty much the same all the brand represents now-a-days is build quality as all the components are the same. I'd shy away from Toshiba though, our resident computer DJ guru and programmer
Our DJ Talk - DJ Help and Resources Chat! - View Profile: SoftJock Rick@@AMEPARAM@@View Profile: SoftJock Rick</title>@@AMEPARAM@@SoftJock Rick says some models have sound driver issues.
Of course aside from that you're going to need an amp and speakers for anyone to actually hear it.
Now are ready for some sticker shock? Take all that and double it. Buy 2 laptops, 2 amps, 2 sets of speakers so that you have a full working backup should one laptop crash or one amp go down and what have you. Personally I'd buy identical systems but if you're tight for money as most new business owners are you can always buy the backup stuff second hand just so you have something in case of failure then replace as your business grows.