error loading nlme package

Hi everyone

The suggestion I received from Mr. Dimitris Rizopoulos and Mr. Gabor
Grothendieck seems to work well. But unfortunately when I am trying to
load nlme package, the following error message is generated. Please
help me on this, at the earliest.

library(nlme)

Error in loadNamespace(i, c(lib.loc, .libPaths()), keep.source) : 
        There is no package called 'lattice'
In addition: Warning message: 
package 'nlme' was built under R version 2.0.1 
Error in library(nlme) : package/namespace load failed for 'nlme'

Though i am using the version R 2.0.0. A couple of hours back it was
loaded, in the new session this problem is generated.

regards
Krishna