I am having difficulty installing the lme4 and ggplot packages

I've tried to install them by selecting a CRAN mirror (have tried several) and then selecting the packages, and have also tried the following;

```
install.packages("lme4",repos="http://r-forge.r-project.org")

```

and 

```
install.packages("ggplot2", dependencies=TRUE)

```

but however I try to call these packages I get the warning message

```
package ‘lme4’ is not available (for R version 2.15.2)

```

or 

```
package ‘ggplot2’ is not available (for R version 2.15.2)

```

the only answers I can find for problems installing these packages suggest upgrading R to the latest version, but I am using 2.15.2 which I believe is the most recent available.

Has anyone else had this problem? 

Any help would be greatly appreciated!!

thanks. 

Lian