Actually, broadband is *not* required, because large data is not required to be sent back and forth. Ping (latency) matters more than bandwidth. Even with 56k, you can have a low ping of under 200 ms.
As long as you have a good ping rate, Kaillera netplay shall be OK.
As long as you don't have an el-cheapo modem nor crappy ISP, your
netplay shall be good. An el-cheapo 56k modem is asking for high ping
rates. I had a major problem that turned out to be my 56k modem that
was causing my pings to be 300+ ms.
Getting a good quality 56k modem will allow pings to be less than 200 ms.
BTW, with the same processor frequency, PJ64k was playable for me and
was able to play Goldeneye 007 with Jimbot using Kaillera, but unfortunately, got desynced in the middle of the Goldeneye 007 gameplay and Jimbot said that Goldeneye 007 is prone to desyncing.
