HashTable Qestion?

Question

I have a question regarding hashtable.
I have a DataBase Table which has three column.
one is the sequence no, then two data fields.
Now I want to populate the hashtable in the same order as it is in the database .The order is very important here.
Then I want the HashTable to search for a particular key and get the value of the next item in the order(not the value of the key item but the next). How can this be done ?
Advice needed.
Thanks