Before running the SETUP.bin, as root:

yum -y install libXp compat-libstdc++-296 compat-libstdc++-33 compat-libgcc-296
cd /usr/lib
ln -s libstdc++-3-libc6.2-2-2.10.0.so libstdc++-libc6.1-2.so.3

It seems like EL 5 doesn't have "xorg-x11-deprecated-libs" but installing libXp does the trick.

./db2setup

ERROR:
The following library files could not be loaded by db2langdir in /mnt/iso0/db2/linux/install/../bin

-> libstdc++.so.5
-> libstdc++.so.5

Check the following web site for the up-to-date system requirements
of IBM DB2 Version 9.1:

http://www.ibm.com/software/data/db2/udb/sysreqs.html

Aborting the current installation ...

Install
yum -y install compat-libstdc++-33

db2setup
/tmp/db2setup.err
Unhandled exception
Type=Illegal instruction vmState=0xb0226c70