[R] retrieve version information for a package?

[Yupu Liang]

Hi,

I am looking for a way to find out the version information of  
installed R packages.
ex:

 >library(affy)
 >SOME_COMMAND_FOR_VERSION(affy)

I know I can do either getRversion() or R.Version() could give me the  
version of R. I assume there must be a way for me to get version  
information for the add-on paclages,right?

Thanks!

Yupu