Future Local time of a place using longitude latitude and datetime

[spummople]

i am developing a travel application.for that I need to calculate the future local datetime of a location using Datetime (a future date),longitude and latitude. (for Eg: i want to calculate the local datetime of a location on August-10- 2010 11.23 AM . Due to the day light saving time the datetime offset may change so i need to convert the august-10- 2010 11.23 AM to local time of the location) I have the inputs longitude, latitude and Date time. i can calculate the current local date using Longitude and latitude but cannot calculate accurately for *future date because of the day light saving time off set* . off set may varies on future dates.i am using asp.net and c# .Can any one help ?