memory question

I just bought a used 2006 Mac Pro that has 4 sticks of 512 memory installed.
There are 2 sticks on one of the memory boards and the other2 on the other board.
Can I put them all on 1 board and then install 1 gig sticks on the empty memory board or do I have to stay with all 512 sticks thruout?
Thanks

You can mix and match but it's really not a good idea. Since memory is so inexpensive it would be better to purchase matched modules and install them in pairs. You should have plenty of room to expand with the Pro.

Regards.