Apparently Octave has been orphaned by the upstream for EL5 , although it is still in Fedora Extras.  It does successfully build from FC6/7 src.rpm packages under CentOS5 beta, albeit with a few additional requirements...

SRPMS:
fftw-3.1.2-3.fc6.src.rpm
glpk-4.13-1.fc6.src.rpm
hdf5-1.6.5-7.fc7.src.rpm
octave-2.9.9-1.fc6.src.rpm
ufsparse-2.1.1-1.fc6.src.rpm

RPMS:
fftw-3.1.2-3.el5.i386.rpm
fftw-debuginfo-3.1.2-3.el5.i386.rpm
fftw-devel-3.1.2-3.el5.i386.rpm
glpk-debuginfo-4.13-1.el5.i386.rpm
glpk-devel-4.13-1.el5.i386.rpm
glpk-utils-4.13-1.el5.i386.rpm
hdf5-1.6.5-7.el5.i386.rpm
hdf5-debuginfo-1.6.5-7.el5.i386.rpm
hdf5-devel-1.6.5-7.el5.i386.rpm
octave-2.9.9-1.el5.i386.rpm
octave-debuginfo-2.9.9-1.el5.i386.rpm
octave-devel-2.9.9-1.el5.i386.rpm
ufsparse-2.1.1-1.el5.i386.rpm
ufsparse-debuginfo-2.1.1-1.el5.i386.rpm
ufsparse-devel-2.1.1-1.el5.i386.rpm

Is there interest in adding this to centosplus?  Or perhaps Dag or Karanbir will pick it up?  I will be building it locally anyway, if it is not available elsewhere, so could help with keeping updated.

Phil