Run a jabber server
OLPC collaboration uses a Jabber server (with a few extra modules and patches) to scale beyond wireless mesh range.
For Give 1 Get 1 users, there is no working Jabber server configured by default, since we cannot handle arbitrary numbers of users on a single server. Look at Community Jabber Servers to see if someone is running a community server you can use.
Then use the Sugar Control Panel to change the jabber server on your XO.
Running your own server
Currently we only recommend running ejabberd with OLPC-specific patches.
The XS School server includes ejabberd.
See Installing ejabberd for instructions on installing and configuring it.
For developers, more details on the ejabberd configuration are here: Ejabberd Configuration
If you get a community server up, consider adding it to Community Jabber Servers.