Hi Sara,
I just filmed a wedding in HDV on my Canon XhA1. My project is in SD widescreen but I edited it in HDV. After reading your post I tried exporting HDV footage for SD 16.9 several times until I found the best settings so try this. File-Export-Movie (export movie)then in the section for settings before saving for export choose VIDEO then PIXEL ASPECT RATIO!! I used D1/DV PAL widescreen 16.9(1.422) then ok. I then opened a new project in Adobe DV widescreen 16.9 etc etc and imported the footage and it fit perfectly without letterboxing on top or botttom which I did not want in the first place. I am using CS3 but if you are using CS4 maybe you should try the media encoder which I generally use for exporting to the web. Hope this is of some help.
Regards Stuart