I have some problem. I have installed gnome 3, and now I have gedit 3.0.6 version. I need to replace it by gedit 2.30.4 version. Any suggestions?
As it has been pointed out, gedit 2.x uses GTK2 and gedit 3.x (supposedly) uses GTK3 so I wouldn't expect it to be easy to downgrade gedit and make it work without uninstalling Gnome 3 and installing Gnome 2 libraries.
Technically, you may be able to download Gnome 2 source code and either compile it with a custom prefix so all Gnome 2 libs go into say /opt/gnome2 and don't mix with the Gnome3 libs or even statically link gedit executable so it's a standalone blob which doesn't use any external libraries. But I think it goes way beyond the amount of effort I'd be willing to spend on this :)
Which brings us to the question: what are your reasons to use gedit 2.x? It's not a particularly stellar or unique editor. Are there any other editors which can be used instead? As a personal suggestion: kate is very good.