If NW does not thru check your bag to DPS if you're on a seperate ticket, then exit the terminal and check into the Crowne Plaza hotel.
NW uses T1, and SQ DPS flights depart T2.
For airport transit hotel info, check:
http://athmg.com/
Please note that there are 3 transit hotels. Best for you to take the one in T1 as I think the little transit train running in between T1 and T2 may be shut after 2am. Otherwise its a long walk to T2.
NOTE: Moving this thread to SINGAPORE forum as transit situation does not really involve SQ, other than the connecting flight.
Guy Betsy
Singapore Airlines Krisflyer forum co-moderator