Pidgin 2.6.1 was released recently and it boasts of support for XMPP voice and video chat features.
That means, finally GTalk like functionality in Pidgin (still not available for Windows though), long after 
Empathy had it implemented through use of 
Telepathy.
There are a few ways by which you can install 2.6.1. My post here, deals with installation in ubuntu 9.04
One way to install 2.6.1 is stated by 
Ubuntugeek. However, due to unmet version dependencies in Jaunty, it installs without the voice/video feature.
There is no PPA for 2.6.1 as of now and the daily builds ppa still has version 2.5.8The 
PPA now has 2.6.1 available. :-)
So, I decided to install from source.
We, first, need to uninstall any previous versions of pidgin.
Open a terminal and,
$ sudo apt-get remove --purge pidgin libpurple
Next, we need to meet some version dependencies,
1). At the terminal,
$ sudo apt-get install python-gtk2 python-gtk2-dev
2). Download gst-python from 
hereI downloaded gst-python-0.10.16.tar.gz ( you can download the latest one)
Go to the directory where you downloaded the file and at the terminal,
$ tar xvf gst-python-0.10.16.tar.gz
$ cd gst-python-0.10.16
$ ./configure
$ make && make install
2). Next, we need to update gstreamer plugins to version 0.10.23>=
To do this, add the following two lines to your 
/etc/apt/sources.list file
deb http://ppa.launchpad.net/gstreamer-developers/ppa/ubuntu jaunty main
deb-src http://ppa.launchpad.net/gstreamer-developers/ppa/ubuntu jaunty main
At the terminal,
$ sudo apt-get update
$ sudo apt-get -u upgrade
This upgrades all your current packages, including gstreamer ones.
3). Download the source for 
libnice, from 
hereI downloaded libnice-0.0.9.tar.gz ( you may download the latest one)
Go to the directory, you downloaded the file and at the terminal
$ tar xvf libnice-0.0.9.tar.gz
$ cd libnice-0.0.9
$ ./configure
$ make && make install
4). Next, we need to install 
farsight 2Download source 
hereI downloaded farsight2-0.0.14.tar.gz ( you may download the latest one)
Go to the directory, you downloaded the file and at the terminal
$ tar xvf farsight2-0.0.14.tar.gz$ cd farsight2-0.0.14$ ./configure$ make && make install5). Now, download the Pidgin 
sourceGo to the directory, you downloaded the file and at the terminal
$ tar xvf pidgin-2.6.1.tar.gz
$ cd pidgin-2.6.1
Next, we need to configure, however, i had to use to following options before configure happened.
--disable-screensaver --disable-startup-notification --disable-gtkspell --disable-meanwhile --disable-nm --disable-perl --disable-tcl
$ ./configure --disable-screensaver --disable-startup-notification --disable-gtkspell --disable-meanwhile --disable-nm --disable-perl --disable-tcl
$ make && make install
This, will install Pidgin 2.6.1. :-)
Now, for the actual Voice/Video feature. To be frank, I haven't got it to work as i would've liked it to. :-(
This works only if the person you are trying to reach is either using the official Google Talk client on a Windows OS, or someone using Pidgin 2.6.1, with Video/Voice enabled on a Linux OS.
Open an IM window,
Conversation --> Media
Here, you have option to either make an Audio, Video or Audio/Video Call.

However, to my disappointment, although I can start a call, the concerned person on the other side, doesn't receive a notification for the same.
So the call is just active locally, it never propagates to the concerned person.
Here's how it looks with a Audio/Video call.

and, with an Audio only call.

In anticipation of a solution, I have reported this as a bug 
here.
Next, I tried to see, if I could receive calls. And here, I was disappointed even more.
Pidgin 
crashes, when someone calls you.
What's worse, the person calling still is able to see an active call on his side, while your instance of Pidgin has crashed.
I have also reported this bug 
here.
So, in the end, I haven't been able to get the Voice/Video chat feature working properly, although, I seem to have come much close.
Oh! And as reported by my friends, you get the "camera"-like status-icon against your name in your friends' chat lists. :-)
Tracking the above two bugs now, seems the only solution :P
Till then,
Cheers!
EDIT:: The bug, wherein your pidgin client crashes has been 
patched and is committed to milestone 2.6.2 :-)