2 easy options:
use logmein's hamachi or a faster vpn client to let them use the QB database on their own laptops (much slower than option 2)
set up a windows terminal server with qb installed and enough terminal services cals to support them- then, one qb install with much faster access to your salesguys. they can use terminal services on Windows, OSX or Linux to connect. server 2003 and cals are cheap, you can support 5 concurrent users comfortably on a dual core AMD/c2d and 2-4 GB ram.
Will it work if I set up a VPN? Or if I use netdrive?