itunes ipsw problem

[websnake]

i was trying to restore custom ipsw using itunes but itunes is not giving me option to browse the ipsw file.

when i click on restore button instead of giving me option to browse ipsw file it trys to connect the apples server and get the update.

how i can get the browse ipsw file option in itunes.

additional info:-

using iphone 3gs (3.1.3)
OS - windows 7
trying to update to 5.0.1

[2k1]

Try holding shift then hit restore?

[websnake]

ok that worked but i am getting error 1600 while restoring

Edit : may be i forgot to enter pwned DFU mode with redsnow.

[2k1]

That's correct should be good now huh?