installed kubuntu, ran updates, installed yum, typed "yum" in console, pressed enter, error: cannot open Packages...

Binary package hint: yum

user@kubuntu:~$ yum
Warning, could not load sqlite, falling back to pickle
rpm: To install rpm packages on Debian systems, use alien. See README.Debian.
error: cannot open Packages index using db3 - No such file or directory (2)
error: cannot open Packages database in /var/lib/rpm
Traceback (most recent call last):
  File "/usr/bin/yum", line 27, in <module>
    yummain.main(sys.argv[1:])
  File "/usr/share/yum-cli/yummain.py", line 75, in main
    base.getOptionsConfig(args)
  File "/usr/share/yum-cli/cli.py", line 170, in getOptionsConfig
    self.doConfigSetup(fn=opts.conffile, root=root)
  File "/var/lib/python-support/python2.5/yum/__init__.py", line 82, in doConfigSetup
    self.conf = config.yumconf(configfile=fn, root=root)
  File "/var/lib/python-support/python2.5/yum/config.py", line 271, in __init__
    self.yumvar['releasever'] = self._getsysver()
  File "/var/lib/python-support/python2.5/yum/config.py", line 383, in _getsysver
    idx = ts.dbMatch('provides', self.getConfigOption('distroverpkg'))
TypeError: rpmdb open failed
user@kubuntu:~$

ProblemType: Crash
Architecture: amd64
Date: Thu May 24 01:47:50 2007
DistroRelease: Ubuntu 7.04
ExecutablePath: /usr/bin/yum
InterpreterPath: /usr/bin/python2.5
Package: yum 2.4.0-3.1
PackageArchitecture: all
ProcCmdline: /usr/bin/python /usr/bin/yum
ProcCwd: /home/user
ProcEnviron:
 SHELL=/bin/bash
 PATH=/usr/local/sbin:/usr/local/bin:/usr/sbin:/usr/bin:/sbin:/bin:/usr/games
 LANG=en_US.UTF-8
PythonArgs: ['/usr/bin/yum']
SourcePackage: yum
Uname: Linux kubuntu 2.6.20-15-generic #2 SMP Sun Apr 15 06:17:24 UTC 2007 x86_64 GNU/Linux