1) Depends on the dialups upload bandwidth. A 56k modem may be able to listen to a 24kbps stream, but I don't think it can source one. Might be able to do a 16kbps or 8kbps. If it's a voice only transmission, this should be fine. Telephone quality.
2) From the DNAS read me:
* 90Mhz or faster server, running one of Windows 95, 98, NT, 2000, ME,
Mac OS X, Sparc Solaris 2.7+, FreeBSD 4.x+, or Linux with a libc6 kernel.
* 14kB of memory for every listener you want to broadcast to (i.e. 1,000
listeners means you need 14 Megabytes of RAM), plus whatever your
operating system needs for overhead, plus 1.5MB for the server's
base requirements. Don't set the listener count higher than you need,
it just screws things up.
* Enough bandwidth to run the server. If you want to broadcast to 100
listeners at 24kbps, you'll need about 24kbps*100 = 2,400kbps = 2.4Mbps
of bandwidth. That's about 2 T1 lines worth of bandwidth. Trying to
push 100 128kbps listeners down your 768kbps cable modem isn't going
Using your own DNAS will save some money but depending on your network configuration and familiarity, setup may be challenging.