All recently manufactured SKUs should be packing the Jasper chipset, including whatever they're calling the Arcade SKU these days. It was a global upgrade.
As for online gaming, it kinda depends what you're playing. Games like Halo 3 are very light on bandwidth consumption - typically around 15-20 MB/hour - while Modern Warfare 2 can run upwards of 30-40 MB/hour. A 384k line should be fine for joining games, but you won't be able host more than one or two players.
An annual subscription is around R400 or so. Once you've registered your LIVE account, you'll get a free month, so check it out then.




