I think you want to capture number of days between 1900/01/01 and another date which is in your table. you can use datediff function.
datediff(dd,startdate,enddate)
for example -
select datediff(dd,'1900/01/01','2008/03/05') gives you 39510
for more - http://msdn2.microsoft.com/en-us/library/ms189794.aspx