Upgrading from:

Statistics`ClusterAnalysis`

FindClusters and the distance and dissimilarity functions have been added to the built-in Mathematica kernel.
SupDistance is replaced by ChessboardDistance.
CorrelationDissimilarity is replaced by CorrelationDistance.
CosineAngleDissimilarity is replaced by CosineDistance.
RussleRaoDissimilarity is replaced by RussellRaoDissimilarity.
A new Hierarchical Clustering Package has been created.

Syntax for FindClusters is the same as in Statistics`ClusterAnalysis` in Version 5.2:

Version 5.2 << Statistics`ClusterAnalysis`; FindClusters[{{1, 2}, {3, 4}, {20, 10}}]

Syntax for distance and dissimilarity functions is also the same as in Statistics`ClusterAnalysis` in Version 5.2:

Version 5.2 << Statistics`ClusterAnalysis`; ManhattanDistance[{1, 2, 3, 5, 10}, {2, 1, 10, 4, 15}]
HierarchicalClustering Package

Many functions from Statistics`ClusterAnalysis` are now found in the Hierarchical Clustering Package:

Agglomerate Cluster ClusterFlatten ClusterSplit DirectAgglomerate DistanceMatrix DendrogramPlot DirectAgglomerate

Syntax for these functions is the same as in Statistics`ClusterAnalysis` in Version 5.2:

Version 5.2 << Statistics`ClusterAnalysis`; Agglomerate[{{1, 2}, {3, 4}, {20, 10}}]