text and dates

Hi, Please Help me!
If cell C5 contains a sent date such as 10/27/01 and Cell d5 contains the text "submitted" when no actual date is available because it was done online. What formula would I use in cell E, which would have given me the number of days lapsed from the date received(Column d) to date sent(Column c). The formula I'm using is IF(D5, D5-C5,""). Since 2 dates are not available how can I get it to ignore the text and not give me the "#value!"error. Is there a possible solution to this, I have tried EVERYTHING!