Hi.
First you have to create the database in Interbase with exactly the same structure as your ACCESS or MSSQL database.
Then, if you're running MSSQL Server 7 there is one feature that can help you move all your data very easily: DTS (Data transformation services)
Otherwise, you can choose to dump the contents of your database to sql statements, or to flat files (CSV for example). And then load them from interbase.
I hope this helps you. There are many ways you can achieve the same thing.
Regards
-Gio-