Excel - Formula

I have a training date spreadsheet that has training start date and end date, some delegates require accommodation the night before and others on the nights of the actual course days. I need to simply translate the night priors and intermediate room night requirements into dates ie

Course start date - 1 December 2009
Course end date - 4 December 2009
Accommodation needed for the night before course start date and during course need to transalete this into date accommodation required ie 30 November, 1st, 2nd & 3 December

I can send the spreadsheet if this would be easier