hmm- well my first advice would be to do a search b/c there are a lot of pr ideas on here....
as far as other ideas... hmm... i was rush chair this past fall... and we did a lot of banners and hung them on the outside of the house (with rush information- and when the girls got in we put congrats etc on them) wearing letters- doing sisterhood dinners in your student center and having everyone wear letters...
have an open party- idk what your rules are on alcohol etc- but its probably been the best way to get our name out there- we started off small and now we have parties with like 300 people and they are teh talk of campus- we've gotten a lot of girls that way too (even boyfriends are like- wow my friend/girlfriend would lvoe it here- i'm going to bring her here blah blah) and we could also celebrate new girls getting in too- by singing them in- or having a party where the new girls invited everyone they knew so to celebrate- THEM getting in...
maybe you could hold a philanthropy/community service event- like we did a daffodil sale for the american cancer society- or d phi e does a twister-a- thon (and this past year they did a jump-a-thon on one of those big blowup jumpy things... but they did it in front of our student union- a lot of people saw them) or alpha phi does a teeter-totter event on their front lawn...
hm.... i don't know what you mean by zeta week- do you mean like a take off of greek week? b/c for that we'd do events with all the fraternities/ sororities- such as a lip synch one night- the greek olympics with silly games antoher... etc
i'mkind of out of ideas at the moment... but if i think of more- i'll let you know
i hope some of that helped