When using tar on Mac OS X, by default it includes all the extended attributes.
The solution I found was in David Olinsky's comment at Jim Plush's blog
For the record, the solution is to set
export COPY_EXTENDED_ATTRIBUTES_DISABLE=true
This worked fine in 10.4 (Tiger). However for 10.5 (Leopard), the option was renamed. Instead set
export COPYFILE_DISABLE=true