If you're going to use VoIP, you don't need any Dialogic, Digium or Sangoma cards. However, it is highly recommended to get a hardware based timer for your system. You can get an x100p card from
http://www.x100p.com for around $29.
If you want to run with 10 agents on a single box using VicidialNOW, here are the recommended specs:
AMD X2 3800 or Intel Core 2 Duo e6400 or higher
2 gig of RAM (4 gig is better if you will use RAMDRIVES)
320 gig HD
x100p card
I would also recommend you wait for the 1.1 final release of VicidialNOW (scheduled this month). This has lots of technical improvements over the previous releases like kernel preemption set to server, fully rpm based system and a graphical installation method among others.