XML Path problem in VB

i've been learning some XML related stuff in Visual Basic, but i have lots
of problems (maybe a bad installation of msxml?)

i can't guess why stuff like position() or .. don't work in the querys

example:

Set nodelist = root.selectNodes("(.//key[text()=""2000""])")

works OK, it gets the node "key" with the text "2000"

but the following doesn't work:

Set nodolist = root.selectNodes("(.//key[position()=1])")

and I always get errors when i try to use things like:

descendant::
child::
..

etc

any help? TIA

note:
i have msxml3 (latest) and 4 (official release) installed