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That looks mighty suspicious - sys_call_table is an internal kernel data structure that holds pointers to the system calls offered by the kernel (these allow user processes to request various things from the kernel). Prior to 2.6 it was an exported symbol, meaning that kernel modules could play around with the system call tables (for instance to provide a wrapper to limit access to certain syscalls). Ever since 2.6, however, this is not possible. It looks like somewhere on your system is a piece of software that depends on the old behavior.
Unfortunately, after doing a bit of googling on that message you have, it seems the most likely answer is that your system has been compromised and a hostile kernel module added (presumable one that tinkers with the sys_call_table, probably to cover its tracks). You need to take the system off the net, carefully scan for signs of an infestation (new accounts you didn't create, funny looking files, etc.), and if it is indeed has been compromised, reinstall from known-good media and apply all of Mandrake's security patches before reconnecting the system to the Internet.
Running chkrootkit or rootkit hunter would probably be helpfull, but that message looks like SucKit, so you may also want to give skdetect a try as well. SucKit isn't a kernel module (though it does act similar to one), so rebuilding the kernel would not work. Fully formatting and reinstalling from trusted media (not from a backup) is really the only solution.
I'm guessing that the system wasn't fully patched either? It's arguably THE most important factor in keeping your system secure. Once you get your new system up and patched, turn off all un-needed services and make sure you have a reasonable firewall. Install a file alteration detector (like tripwire) and make sure to keep up with patching.
To be sure it is removed you'd rather need to reinstall. Use your Mandrake installation cd as rescue disk and copy your important data to any other partition. Then reinstall, turn off all services you don't need (if this is a desktop machine you usually don't need any) and configure your firewall.
I'm also moving this thread to Linux-Security.