improving search form

I find the search form not that pleasant in use sometimes. I fill in a search value but forget to click the right radio button.
A great solution would be to have just one select box to select what to search on, together with a single fill-in field, which changes to a select box when the search context is a list (Instead of a page refresh to change the fill-in to a select box, AJAX could be used...). I understand that this is quite some work, so another solution would be to auto-select a radio button when its field is clicked.
both of these ideas will get in the way of a possible future idea of making a feature to search on multiple user properties. Fot this a solution would be to have checkboxes that get auto-checked when their input is filled in.