OK. Perfect. First, please don't get foscam, they are junk. What are your needs? Indoor, ourdoor, audio, ptz. what are you trying to cover?
As far as pc, there are tons of options for slim desktop pc's that are quiet and will be perfect for 3 cameras. Here is one great option
http://www.ebay.com/itm/HP-EliteDes...1243774641?pt=Desktop_PCs&hash=item2336d4dab1 note that that model does not have room to add a second hard drive and the drive in there is a laptop 2.5....model has a 3 year next business day warranty....cannot beat that price...there are other options from the dell outlet as well. The hp I linked to is the latest haswell processor.