Though Houdini and other packages have support for metaballs, creating more than a VERY small number will typically cause most machines to grind to a halt. This is unfortunate as attatching metaballs to particles is a great way of getting fluid effects.
Fortunatly as of recent implementations of RenderMan support blobby objects as primitives RiPtoB allows the animator to work completly with points, render these AS POINTS from houdini, then convert them to Blobbies before they get to RenderMan.
To use riPtoB from Houdini simply set an object to "Render As" points at the obj level. Then in the output driver set the render command to be "riPtoB | render". You can use the Point sop to set the "scale" attibute which sets the size of each blobby. Colour and other point attributes should also be converted.
Download riPtoB for SGI and FreeBSD.
NCCA, Bournemouth University