CPU doesn't matter much, you won't gain anything with a SMP box.  Spend
your money on F A S T disks or perhaps multiple load balanced machines
instead.

RAM isn't a big deal either until you get to high concurrent stream
counts -- WMS keeps a re-transmit buffer per connection; more
connections = more buffers.  2GB is plenty for multiple thousand.

Basically, it boils down to bandwidth.  Assuming you have GigE, and
300kbps streams the rough math works out like this:

1000 / .3 = 3333 concurrent streams.

This assumes a PERFECT network (impossible) and no stream delivery
overhead (also impossible).  I would go with something a bit more realistic:

(1000 *.7) / (.3 * 1.2) = 1667 concurrent streams.

This allows for 70% network utilization and 20% overhead in the stream
delivery (retransmissions, protocol overhead, etc).

So then, your disk I/O would need at least:

1700 * 300kbps = 510Mbps

IDE isn't going to cut it. ;-)  I've done systems of this magnitude
using FiberChannel attached EMC storage arrays into Compaq Proliant
boxes.  In my case, I was using multiple 100Mbps NICs, but the concepts
are the same.

T.