I can answer that. A loser tried his luck at a DDoS attack on Bigpond's backbones about a year ago. Some changes (I can't say what they are for obvious reasons) were made to the network to prevent the network from faltering should the same happen again. For some odd reason this affected DNS in some cases and dialup users, depending on their location, find it hard to access the NSW server. You should be able to access the QLD or VIC servers though with no problems.
... are the individual server addresses. The VIC server is about to be replaced with a new one as part of a complete network infrastructure upgrade so it is redirected to QLD for the time being. Let me know how you go.
By the way, not receiving a reply to a ping does not necessarily mean that the node is unavailable. Having said that, I do get responses:
Pinging nsw-irc.bigpond.com [184.108.40.206] with 32 bytes of data:
Reply from 220.127.116.11: bytes=32 time=133ms TTL=121
Reply from 18.104.22.168: bytes=32 time=123ms TTL=121
Reply from 22.214.171.124: bytes=32 time=121ms TTL=121
Reply from 126.96.36.199: bytes=32 time=127ms TTL=121
Ping statistics for 188.8.131.52:
Packets: Sent = 4, Received = 4, Lost = 0 (0% loss),
Approximate round trip times in milli-seconds:
Minimum = 121ms, Maximum = 133ms, Average = 126ms
If you still have problems you may need to post further information about your connection here.