Well, kernel compilation requires some dev packages+kernel headers.
First of all run apt-get build-dep linux-source-2.6.26

In your case, even if I am not a danish motherlanguage :-) , you miss zlib1g-dev package
For other possible missing (header) files have a look at http://www.debian.org/distrib/packages.en.html#search_contents, you can easily find the package the file belongs to.

Furthermore I suggest you to look at http://kernel-handbook.alioth.debian.org/, there are plenty of information for every debian kernel related question.

raffaele


2009/1/8 Svend-Erik Kjær Madsen <sv-e@sv-e.dk>
Hi

I work with the kernel issue now, but seem to be stuked in a
documentation fault.

<cut>
make[1]: Forlader katalog '/usr/src/linux-source-2.6.26'
/usr/bin/make  EXTRAVERSION=-rt-200811111930  ARCH=i386 \
                            -C Documentation/lguest
make[1]: Går til katalog
'/usr/src/linux-source-2.6.26/Documentation/lguest'
cc -Wall -Wmissing-declarations -Wmissing-prototypes -O3 -I../../include
lguest.c  -lz -o lguest
lguest.c:34:18: error: zlib.h: Ingen sådan fil eller filkatalog
make[1]: *** [lguest] Fejl 1
make[1]: Forlader katalog
'/usr/src/linux-source-2.6.26/Documentation/lguest'
make: *** [debian/stamp/build/kernel] Fejl 2
</cut>

Sorry for the Danish version of my Lenny but it's there I live ;) it's
all about a missing zlib.h and lguest.c  What do I need to install
beside the kernel source and the rt patch, before I can make the
rt-kernel, some kind of documentation source ?

Thanks in advantage, and for reading

/Sv-e