You are suggested to build Slackware packages in this order:

freetype (upgrade Slackware 12.1 package to have BYTECODE INTERPRETER enabled)
rarlinux
flash-plugin
divx4linux
crystal-project
crystal
polyester
gtk-engines
cabextract
libsigc++
skype
sqlite
libcap
portaudio
jack-audio-connecion-kit
libsndfile
vcdimager
lame
twolame
xvidcore
libdvdnav
libdvdcss
libdvdread
libdvdplay
libdvbpsi
lsdvd
check
liboil
speex
libdv
djbfft
faac
faad2
amrwb
amrnb
libdca
libgsm
id3lib
yasm
liba52
x264
libebml
libmatroska
imlib2
libraw1394
libdc1394 (Use version 1.2.2 if you want libdc1394 support in vlc)
libavc1394
libiec61883
dirac
schroedinger
libnut
ffmpeg
libmpeg2
libmpcdec
smpeg
openal
libmpeg3
gstreamer
gst-plugins-base
gst-plugins-good
gst-plugins-ugly
gst-ffmpeg
mpeg4ip (Remove FAAD2 before building MPEG4IP and rebuild FAAD2 after successfully building and reinstalling MPEG4IP)
win32codecs
live555
mplayer
mplayerplug-in
smplayer
kaffeine
streamripper
fftw
libsamplerate
libquicktime
realplayer
opera
libotr
pidgin-otr
k3bmonkeyaudioplugin
aircrack-ng
libmspack
terminus-font
wxgtk
libnotify
libupnp
libdaap
libopendaap
libgii
libggi
libshout
xosd
vlc
moodbar
wine
adobereader
dclib
valknut
avifile
libfame
d3lphin
kftpgrabber
konversation
kopete-otr
mjpegtools
murrine
pptp
soundkonverter

Please, respect packages requirements described in slack-required.