Ubuntu has packages at http://getdeb.net, but there is a conflict with gimp-python. This package was included into gimp-data, but ubuntu-desktop depends on gimp-python. 🙁 EDIT: If you have messed up your installation while trying – just install 2.6.0 over it like described here.
If you get complaints about gimp-python, then you have messed up your installation with doing something else as “dpkg -i *” in terminal. Just deinstall “gimp”, reinstall ubuntu-desktop (no harm done) and install 2.6.1 with dpkg. Worked for me.
From PhotoComix comment to the last posting:
…and for Ubuntu a short but updated how to compile guide is here
http://www.gimpusers.com/news/2008-10-07/compile-gimp-260-for-ubuntu-804.html..is for 2.6 but for 2.6.1 nothing change except the source code to download
For windows i suggest to avoid to try to use the help with the web browser, that may crash gimp, (on my 2 PC that always crash gimp )