I can't believe that simply running Opera would cause the kernel to crash!
The X Windows GUI - maybe. The kernel ... I really doubt it...
Q: Did you deinstalling 10.5 and installing a newer version:
yum install opera-10.10.gcc4.shared.qt3.i386.rpm
Q: Did you get a specific message in your system log (/var/log/messages)?
Q: Have you tried a "yum update kernel"?