Windows locale setting / Regional settings Options in Control Panel & affecting datetime dataentry

Hello Experts
I wish i could give this question more than 1000 point !!!!
Briefly
I have an application developed by VB.net & SQL server 2005 as database
The application has many forms that contains a Textboxes  to accept a date from  the end user , My purpose is to enforce all Date entry to be in specific format  dd/mm/yyyy
Suppose i have 10 users that using this application and each user has diffrent  Regional settings "Date setting" Options in Control Panel  
My questions is
1- in Database level "sql server DB" , How can i specify the format For DATETIME column to be in dd/mm/yyyy ?
2- in application level , Is Windows locale setting / Regional settings "Date setting" Options in Control Panel  will affect  on the date format that the user will enter? IF Yes
how can handle any problem may happen if user enter 07/17/2008 instead of 17/07/2008?
Please note that the calender control many users complains after using it for many reasons ? so please dont suggest to use this control as a solustion !!
Thanks