I'm guessing this person has moved on...but I'll say it anyway (DCT has good info, but I'll add a little in "for dummies" mode):
the idea behind navagativing around in zork and other text based games is that you have an action you want to perform, and a VERB and a NOUN will get you far. You can say "look at the sword" but you can also say "look sword" and it will understand you. While you can say "go north" you can also just type n and the game will know you want to go north. N = north, S = south, u = up, d=down, ne = northeast, and so on...
LOOK at everything. If it isnt nailed down, you should probably take it. Take your time, read and re-read all the descriptions...let yourself "see" what your character sees. If you arent sure of something, LOOK AT <whatever it is>. Open things, move things, push/pull things....dont be afraid to play around with objects. If its in the description, it may be there for a reason...
If you are attempting to do something, and you cant...rephrase what you want, try using a different word. If the game doesnt understand you when you say "move the bookshelf" try "pull bookshelf" "push bookshelve" or even "open bookshelve" (if you think its part of a secret passage or something).