just do this
Go to Run->Cmd->
write->Net Stop Mssqlserver (or just shut down ur sqlserver 4 a while from
SQL Server Configuration Manager)
(After ,it has Stopped)
Go Tothis Direcrtory:-----
C:\Program Files\Microsoft SQL Server\MSSQL.1\MSSQL\Data
here in data 2 files of ur database are stored(in my case Tradenbids)
1. Tradenbids.mdf
2.Tradenbids_log.ldf
Copy these to file
and paste whaere ever you want
Now
Go to Run->Cmd->
write->Net Start Mssqlserver (it will start mssqlserver)
now u have the whole db , just copy and paste these to file whenever u want a backup