It's an cross-platform opesource application thus not only in GNU/Linux but you can use it in MS Windows and Mac OSX as well. Once installed you'll have to load your image file and then follow its "5-step" process and then it'll split your raster image and create a PDF file by using which you can easily print your poster since each page in the PDF contains a "cut" of the original image.
*. It's written in the FLTK tool-kit thus uses its own "theming" which doesn't integrate that well under Gnome nor Qt/KDE... but as soon as it gets the job done, who cares!.
*. Once loaded, it'll display information such as the raster image resolution, DPI, size and color type.
*. Supports a huge list of raster images such as: BMP, DDS, Dr. Halo, GIF, ICO, IFF, JBIG, JPEG/JIF, KOALA, LBM, Kodak PhotoCD, PCX, PBM, PGM, PNG, PPM, PhotoShop PSD, Sun RAS, TARGA, TIFF, WBMP, XBM, XPM.
*. A five step wizard type process is involved which lets you: Change the PDF pages size (A4, letter, Tabloid, etc), overlap settings, image splitting, etc.
Well, that's about it actually. When done all that, you can save the split raster image into a PDF which can be sent into printing later.
You can install PosteRazor in Ubuntu 11.04 Natty Narwhal, 11.10, 10.10 and 10.04 by using the below command in your Terminal window.
sudo apt-get install posterazor
That's it. Good luck.