Small Office setup, request feedback

Trying to get a new phone system off the ground for a small office I work for. I have the following PC hardware to work with and was hoping to get input on whether it would do the job or if I needed to add anything extra to it:

AMD 64bit Dual core CPU
2gb ddr400 memory
300+gb disk space (disk1: SATA 82gb 7200rpm, disk2: SATA 250gb 7200rpm)
Creative sound blaster audigy card (onboard sound disabled)
10/100 onboard NIC (can get gigabit if better suited)
onboard video (have PCI-E video card available if it can/should be used for some GPU processing tasks)

What this would power:
Voice only, 2-3 incoming numbers w/some direct and one to menu system for reaching various offices (billing, front desk, etc).
up to 5 simultaneous calls/connections to the outside world
10-20 handsets/extensions
hold music
other tidbits I am missing/not thinking of?

I got the AsteriskNOW cd installed, but am not sure where to go from here. Also, for providers of the VOIP connection to the outside, are there any recommendations/input about companies/plans that would do well for a system with the needs I have described above?

With that hardware you can have 50-100 simultaneous calls…

first of all you achive all your requirement by using asteirks.
you can go upto 50 to 70 concurrent calls with that server with recordings,voicemail…etc

you can connect the outside world in the following ways

  1. voip account either SIP/IAX ( u need a voip account and broadband )
  2. PRI E1/T1 ( u need digium digital cards to connect them)
  3. pots line ie:analog line ( u need digium analog cards)