[R] Upgrading R means I lose my packages

[James Milks]

The title says it all.  Does anyone know of a way to save your  
packages when you upgrade to a new version of R?  This may seem petty,  
but I'm accumulating enough packages that having to download and  
install each of them anew every time I install a new version of R is  
rather of a pain.  Ideally, I would like the new version of R to  
recognize the packages I've installed on the previous version without  
needing to reinstall the packages.  Is that possible?

My system: Mac OS 10.5.4.
Current R version: 2.7.1

Thanks for any suggestions.  My apologies if this has been answered  
before and my search missed it.

Jim Milks

Degree Candidate