I have used an update sql statement to change a table of sqlserver 2005 and I want to bring it back to its former state. can I rollback the table somehow?

By default SQL Server runs with implicit transactions. Unless you declare a transaction with BEGIN TRANSACTION, the update is automatically committed. If you did issue a BEGIN TRANSACTION before your update statement, you can issue a ROLLBACK TRANSACTION command, and the data will return to its original state. If not, then you will have to look at restoring the database to recover any lost data.