Dec 2008 and Jan 2009??
It is worth bearing in mind that this is HIGH season......Xmas is extremely crowded everywhere and choice will be restricted..... you may find it quite difficult getting anywhere by just turning up.... especially somewhere nice.
New Year is the biggest Thai holiday after Song Khran and many places are RAMMED - transport, accommodation and everything is overstretched.
Many budget places DO have web sites...it's not as if they are an expensive thing these days...they may not subscribe to a central booking site so just get a map and google the area you fancy....a phone call is usually sufficient....be prepared for zslip-ups aND MISTAKES AROUND THIS HOLIDAY SEASON THOUGH.
If you are going to be late..LET THEM KNOW!!!
(I really think if you come to Thailand it is ESSENTIAL to bring your mobile and spend 50 baht and get a SIM card...this will save you so much time and hassle.