Form <select> field problem

Hi I may be posting this to the wrong place, and if so I apologise. If someone knows of a better place to post my query please tell me, and I will. :) This problem is about 50% PHP and 50% Javascript, really to do with how the two interface with each other. Anyhoo, down to the problem. I have a Select form item with 'multiple' set. It sends an array of values to be dissected and applied to database tables, hence it's name value is 'groupchoice[]'. This all works well and good when some value(s) are selected, but obviously gives an error if the form is sent with no value selected. What I need to do is come up with an elegant way of stopping the form if no entries have been selected (or indeed if all entries have been deselected). I have successfully used a Javascript function to do this, but it only works if the field is named 'groupchoice'. The part of the function that is causing the problem is listed below: if (!document.existing.groupchoice.selectedIndex != "") //this works if (!document.existing.groupchoice[].selectedIndex != "") //this gives a syntax error Obviously if I call the field 'groupchoice' the information sent is no longer an array, and therefore I cannot have multiple selections, which is imperative. I have thought of other ways of doing the job, such as having an alert pop-up if there is an error and then return them to the form, as opposed to before the form is sent, but didn't feel that this was very elegant. Have any of you PHP gurus out there experienced this kind of problem and found a solution? I would be greatly appreciative if someone would share their expertise. TIA Keiran keiran@wynyard.net