user selectionz ?????

hi guyz im making this report generation form which lets the user select a category out of 8 through a dropdown list then the user has to select a few more thinggs only then the report can be generated now my problem is each of the 8 categories has 3 to 5 sub-categories what i want to do is when he selects a category the sub-cat-dropdown should get the sub-cats of ONLY the category selected n i have no clue how to go about this decently that is without having to re-load the page when category is selected suggesstion .... solutions pleeeeeeez thnx a million toby ..... __________________________________________________ Do You Yahoo!? Everything you'll ever need on one web page from News and Sport to Email and Music Charts http://uk.my.yahoo.com