You can take a mini-bus from Victory Monument (near the Pong Lee Restaurant) to Nakhon Sawan (stops at the Big C supermarket) for 205 baht one way and takes approximately 3hrs.
There are also several regular air-conditioned buses running daily between Bangkok and Nakhon Sawan. For more information, you can ontact the Northern Bus Terminal at Mo Chit (Tel. 66 2279 4484-7) for details. Time approx 4hrs. The Nakhon Sawan bus station is to the west of the city centre: 15.7017 100.1186.
If coming from the North (in this case in Nov 2010, Lampang) the bus takes 5 hours and costs B280.
A bus from Suphanburi will cost B90 (non aircon), will take 4 hours, and wander all around the countryside on the way there.
The Northern Line trains run many times a day from Bangkok through Nakhon Sawan and ends in Chiang Mai. For more information, please contact the Travel Service Division at tel. 66 2223 7010, 66 223 7020
The train station is a little out of town, ~6kms. Tuk tuks are waiting to take you into town.
Wat Worranatbanpot [http://www.probuddhism.com/appeal.html], Thammavitee Road, Amphur Muang