Ok, it bothered me that I couldn't figure out the "find or create resource" code so I got Lizard to help me out.
Code:
tell application "OmniPlan"
-- This probably doesn't work in 1.1 beta 1 and earlier releases
set myDoc to open "Users:tom:Desktop:PlanTest:foo.omniplan"
-- The following, commented out code is the workaround
-- open "Volumes:Extra:Users:tom:Desktop:PlanTest:foo.omniplan"
-- set myDoc to document "foo.omniplan"
tell myDoc
set myToms to resources whose name is "Tom"
if (count of myToms) > 0 then
set Myself to first item of myToms
else
set Myself to make new resource with properties {kind:person, efficiency:2, name:"Tom", cost per hour:200.0}
end if
set MyTask to make new task with properties {name:"Cure Cancer", duration:8.0}
assign MyTask to Myself
end tell
end tell