[update Nov 11, 2006: here is a link to the section on Cutom Items from the v2006 manual: www.empirisoft.com/medialab/help/custom_items.htm]
Custom items are way easier than they were in v2004. You create a web page using whatever program you like. If it shows up in Internet Explore then it will work fine. You can include any html form techniques you like for as many variables as you like. Just make sure your form uses "method=post"
List the item as a custom item in your questionnaire, indicating the name of the file in the filename field. MediaLab will present it and will intercept any posted data and save it to your data file so long as the posted variable name exists in your experiment somewhere as an item. If you have multiple variables in a single custom item, then just create extra custom items with the additional variable names needed.
I've posted a sample here that uses radio buttons. Let me know if you have any trouble with it.
Note this sample requires v2006.1.34 or later.