Hola
Friend of mine uses HP 6715s notebook with ATI Radeon x1250 card.
The first problem he met was unability to run X at all...
I'm currently using backtrack for two years, and never had any radeon card,
so that was fun for me 
First, the driver posted:
wiki.remote-exploit.org/index.php/Modules
Has incompatible Application Binary Interface and only fits for BT2... 
The following script will do all the dirty things for you:
(tested at least on HP Compaq 6715s)
Code:
#!/bin/sh
# Distributed under the terms of GPLv2
# Author: Bohdan Turkynewych, 2006-2008, tb0hdan@gmail.com
driver_files=`ls ati-driver-installer* 2>/dev/null|head -n1`
function stale_cleanup() {
slack_packages=`ls fglrx-* 2>/dev/null`
if [ "${slack_packages}" != "" ]; then
echo "Performing stale packages cleanup..."
rm -f fglrx-*
fi
}
#
stale_cleanup
#
if [ "${driver_files}" != "" ]; then
./${driver_files} --buildpkg Slackware/All
else
echo "No ATI driver files found."
echo "Please get one on ati.amd.com/support/driver.html"
exit 127
fi
slack_packages=`ls fglrx-* 2>/dev/null|head -n2`
if [ "${slack_packages}" != "" ]; then
# unpack modules
moddir=`mktemp -d -p /tmp 2>/dev/null` || exit 127
tar -xvzpf fglrx-module* -C ${moddir}
# unpack x driver
xddir=`mktemp -d -p /tmp 2>/dev/null` || exit 127
tar -xvzpf fglrx-x* -C ${xddir}
#
cat ${moddir}/install/doinst.sh|grep -vP '^#' >> ${xddir}/install/doinst.sh
echo "" >> ${xddir}/install/doinst.sh
echo "aticonfig --initial --input=/etc/X11/xorg.conf" >> ${xddir}/install/doinst.sh
package_dir=`mktemp -d -p /tmp 2>/dev/null` || exit 127
curdir=`pwd`
cd ${moddir}
cp -vfR ./ ${package_dir}
cd ${curdir}
cd ${xddir}
cp -vfR ./ ${package_dir}
cd ${curdir}
rm -rf ${moddir}
rm -rf ${xddir}
cd ${package_dir}
mkdir -p usr/bin/
cat << EOF > usr/bin/aticfg
#!/bin/sh
olddir=\`pwd\`
cd /
sh /install/doinst.sh
rm -rf /install
cd \${olddir}
EOF
chmod 755 usr/bin/aticfg
cd ${curdir}
dir2lzm ${package_dir} ${curdir}/ati-fglrx.lzm
rm -rf ${package_dir}
fi
stale_cleanup
For the lazy ones: Get file box.net/shared/1drtone5ce#oss
Note: Paranoid sneaks should use script instead, and they can unpack lzm and verify it as well 
Now, how to proceed
1. Put lzm file on modules/ directory on your usb stick
2. Boot BT3 in Text mode with frambuffer
3. type: aticfg
4. type: kdm
Voila
Any comments, mods, fixes, beer are welcome 
Keep your gunpowder dry, and Backtrack running
Happy auditing.
WBR, Bohdan Turkynewych, SSA