Win Server x64/R: Memory Allocation Problem

Dear all,

how can I use R on a 64-bit Windows Server 2003 machine (24GB RAM) with more than 3GB of working memory and make full use of it.

I started R --max-mem-size=3G since I got the warning that larger values are too large and ignored.

In R I got: 

memory.size(max=FALSE)

[1] 10.5

memory.size(max=TRUE)

[1] 12.69

memory.limit()

[1] 3072

but when I run the next command, I get an error:

climb.expset <- ReadAffy(celfile.path="./Data/Original/CLIMB/CEL/")

Error: cannot allocate vector of size 2.4 Gb

Here is the R version I am using:
platform       i386-pc-mingw32              
arch           i386                         
os             mingw32                      
system         i386, mingw32                                       
version.string R version 2.11.1 (2010-05-31)

What can I do?