You may find it a bit of a challenge to get Reporting Services 2008 to repeat table headers across pages. Unfortunately the tablix properties 'Repeat Row Headers' and 'Repeat Column Headers' appear to do absolutely nothing despite what MSDN says. In fact there is a connect request related to it here. There is a bit of information on the web about this - but not definitive guide and I still found myself scratching my head a bit, so here's my attempt at explaining it:
Select the tablix in question and click the arrow on the left of Column Groups and the bottom of the Design tab, and select 'Advanced Mode':
Under 'Row Groups' you should now see grey bars before and after each tablix grouping marked '(Static)'. These represent the column headers for each group. Click on one of these:
Click the Properties Window (there's no right-click menu on the static groups). On the RepeatOnNewPage property click 'True':
Repeat step 3 for every static group that a repeating header is required. Bear in mind there are the static groups after the tablix - don't set these to repeat.
Then you should be done! Shame this can't simply be done on the tablix property - lets hope MS fix this in a Service Pack at some point.