You are correct. I apologize that I didn't post my solution. I am running around trying to prepare for the installation of our new phone system (which is partly why I was trying to trunk in the first place). This is how I solved it. (not that this is the best or only solution)
I used the web interface on both the Procurve 2900 and the procurve 1800s (mostly because the 1800 does not have a CLI).
I added a number of ports on the 2900, 4 to each 1800 in my case, to a trunk group and choose LACP as type. In VLAN configuration I could add the trunks to any vlan as tagged.
On each 1800 I created each trunk using the LACP setup utility. I then created the vlans and added the trunk to each. I think they add automatically, but it never hurts to check. Where I was running into trouble was on vlan port config. The help directs you to connect to other switches by choosing "tagged only" and "none" for PVID, but every time I set it that way I had to go plug to the switch and change it back to "all" and choose a PVID. The kicker is you can only choose one PVID. If a port was set to the PVID of the vlan it was isolated.
What I did was set all ports to the untagged PVID and shoose "all" for packet type. Then I had to set the nic in the server to be vlan capable. After that- everything fell into place.