Would it be a surprise to you if I say that I don't know how Tally ERP works and, frankly, don't have a little desire to learn about it? If you need to have some data storage in your own system (as I understand, it is not related to Tally) and don't want to rely on any available DMBS, the simple logic should tell you that you should be the one to develop such database system, or some other data storage and retrieval system.
Nobody will be able to give you a definitive advice based on your information, when we have no idea what you are your goals. In some simplest cases, it could be as simple, as, for example, a single XML file fully loaded in memory. Is this could be the case, I would strongly advise to use
Data Contract:
http://msdn.microsoft.com/en-us/library/ms733127.aspx[
^].
I don't know why do you have such strong objections against databases and prerequisites. It could be something light weight and open source, which would not be too heavy prerequisite. To chose from, please see:
http://en.wikipedia.org/wiki/List_of_database_management_systems[
^].
—SA