Oh man - sorry - it's OK - I realised I wasn't moving the record pointer so I was trying to reload the same line each time through - here's the working code...

select navigator
* loop through all the records
for intLoop = 1 to reccount('navigator')
goto intLoop
strGroup = alltrim(navigator.na_group)
strName = alltrim(navigator.na_name)
strGraphic = alltrim(navigator.na_graphic)
strIdent = alltrim(navigator.na_ident)
* test each record to see if it's a topnode
if navigator.na_topnode = .t.
.oleTree.nodes.add(, 1, strGroup, strName, strGraphic)
else 
.oleTree.nodes.add(strGroup, 4, strIdent, strName, strGraphic)
endif
endfor

Cheers!