Pidgin v2.0(.1) provides no easy way to change the key bindings (this is intentional) so you can use [Ctrl]-[Enter] to send your message rather than just [Enter] to send a message. This is a problem for me as I usually like to make my sent messages intentional rather than typing something I’ll regret and fat-fingering the [Enter] key.

Since I use the portable version of Pidgin the file to edit is: X:\PortableApps\PidginPortable\Data\settings\.purple\gtkrc-2.0

Its contents should be the following:

binding "pidgin-bindings"
# enter inserts a newline
bind "Return" { "insert-at-cursor" ("\n") }
# ctrl-Enter sends message
bind "<ctrl>Return" { "message_send" () }
widget "*pidgin_conv_entry" binding "pidgin-bindings"