Hi,
If you are using Jamoma 0.5.7, it only works with Max in 32-bit mode. I believe Max 7 starts as a 64-bit application by default on OSX.
If you are using Jamoma 0.6, it's just a regular package, and you should be able to install it into your "~/Documents/Max 7/Packages" folder in the same way as for other packages.
BTW I have just uploaded a new 0.6.0 alpha version to the Jamoma web site.
Cheers,
Trond