Hi Paul,
There are few option available to do that.
1. Put the page in Edit mode then go to the web part menu (verbs) and select Connections.
4 options show up, 2 are obsolete and the other 2 are Get Row From and Send Row To. Pick what's the most appropriate for you.
Then a wizard shows up that would help you to complete
2. Another option would be to use the Session.
Please check the documentation regardig to this topic.
If you have any questions please let me know.