We are using sql server 2005 and accidentally deleted table rows from database. We tried restoring .mdf/,ldf files from last night backups but these files are not getting backed up because they are constantly in use.
Is their any open source tool available i can use to restore these deleted rows in a table?
You should be doing a SQL backup, then making a backup of that backup file. If you haven't been doing that, there's little chance of recovering your data.
Depending how you have your DB setup, you *might* be able to recover by rolling back changes from the log file. But it may be too late at this point. I don't know of any open source tool for that. A DBA with more experience than I have may be able to do something.