Just like I said the script will be in public use. So if some user wants to use checkboxes to find out other peoples interests he/she might use checkboxes.
At this address is one example (Interests):
http://edit.yahoo.com/config/eval_register
Most of the users propably don't know anything about PHP, so it would be best solution if the field names just could be written without '[]'s. I think many just would forget to write '[]' at end of the name.
If someone is familiar with perl I think he/she knows what kind of method I am trying tell. (Creating the list when parsing the fields).