I need one really important package from oneiric to be installed (upgraded) on natty.
How can I extract just single deb file? (64 bit).
Should I use backports? if yes, can you please tell me how to set the backports from oneiric?
I think this is not good idea. Oneiric is still alpha version and many packages are broken or unstable. You can also have many problems with dependecies.
Which package do you need? Maybe there is a PPA with newer version.
General howto for backports -- https://help.ubuntu.com/community/UbuntuBackports
While I stress that this probably isn't a good idea, you can download the package you mentioned in the comment here.
Then, to install it, run the following:
Please, again, this is likely to break things, because this is a