Ubuntu Netbook remix for Atom N450 64bit

Install the desktop (or even minimal) 64bit ubuntu then install the metapackage once installed. The performance is not reduced outright, The 64bitness only helps you address more ram as well as give a boost to CPU intensive things like video / audio encoding. If you intend to simply web browse and chat and have less than 3Gb RAM then 64bit won't give you anything noticable.

what the name of "metapackage". What benefits (exept enviroment view optimized for small screen/resolution) it gives? Do I need additional packages to increese time of work from battary. What the packages can help me easy manage score of performance|time_of_work. Is there any benefit to use of alternative kernels such as "kernel without timer interrupts with only on demand interrupts" for example.

The metapackage gives an easy way to install a whole bunch of packages to achieve an end. For example if you install the minimal iso then want to get the full desktop you would have to install ALL the packages that make it up, or you can just use ubuntu-desktop and it will all be handled. This is also the case with ubuntu-restricted-extras it installs a lot of packages but you can install them individually if you so desire. It just makes things easier

The battery will be managed by ACPI but you can install a lighter desktop and windows manager, something like LXDE and Openbox will stress the CPU less and so use less power. Using a full Gnome desktop with desktop effects uses more power.

The rt kernel is ideal for music engineers and graphical designers, if you intend to web browse / chat and game then you should use the default kernel. You can make the kernel more efficient if you recompile it with options closer to your needs but with your clear ewness to the OS, I wouldn't advise it at this stage.