[R-sig-Geo] Problems generating RasterStack object

[Gerardo]

Hi all. I have a set of Raster layers I want to use to generate species 
distribution models. Initially the files had all different projections, 
resolution and extent. So i resampled and cropped them with a mask layer 
with the extent I wanted. All was done in R. After the processing only a 
few of the layers had the same extent and so they couldn't be stacked 
with stack(files). I also tried creating an extent object with the exact 
extension I wanted, but nothing worked, most files ended up with some 
degree of error. The quick=T argument returned another error that said 
the a character string was expected. Is there a function or a procedure 
to equalise the extent of all the layers?

Regards
Gerardo Martin