I don't know what vB 2.2.3 is like but it's probly the same as 2.2.5...anyways, go to
User Profile Fields and click
Add. Fill it out and when you get to
Field required?, check
Yes and that field well be required, now to hide it, look for
Field hidden on Profile? (should be right below the field required one) and click
Yes (that'll hide it on the profile

). to add something from the field, you have to find out the field id is then go into your postbit template and add
$post[field#] (remember to replace
# with the field ID Number (which can be found when you put your mouse over the edit button for editing the field, look at the status bar and you should see something like fieldid=#

)

) hope this helps