noob question about using rsync on a network

[ttx336]

I am trying to setup rsync to backup one of my WinXP machines; if I can get this working I want to then set up a cron job to run the backup automatically. I can get rsync to work just fine on the local machine but I can't figure out how to address the remote machine that I want to backup.

I tried using

rsync -av hplaptop:Gary/Documents /root/Documents

and many variants of that but no good. I also tried to access my other Fedora machine from this one as a test but it didn't work either.

I can transfer files back and forth among all of these machines so my network seems to fine.

The error I get is ssh: hplaptop: Name or service not known

Thanks in advance,
Gary