How be sure user enters the 1st date of a month, quarter, or year in a date field on a form

I have a date field on a form named txtStartDate.  I want to be sure the user enters the 1st date of a month, quarter, or year in the field.

I also have three checkboxes on the form...  chkbxMontlhly, chkbxQuarterly, and chkbxYearly.  Only one can be selected.

So in other words...

If they have selected chkbxMonthly they have to enter either 1/1/xxxx, 2/1/xxxx, 3/1/xxxx, 4/1/xxxx, 5/1/xxxx, 6/1/xxxx, 7/1/xxxx, 8/1/xxxx, 9/1/xxxx, 10/1/xxxx, 11/1/xxxx, or 12/1/xxxx.

If they have selected chkbxQuarterly they have to enter either 1/1/xxxx, 4/1/xxxx, 7/1/xxxx, or 10/1/xxxx.

If they have selected chkbxYearly they can only enter 1/1/xxxx.

How can I do this?