many markers on a map

Hi all. Currently I have a loop which loops through the xml file
adding markers to the page, each marker on its own overlay. This is
giving me very slow results as I have some 600-700 markjers. I know
that this is to many and I am working on a way to reduce this, however
for short term purposes I need to speed this up.

Is it possible to add all the markers onto maybe 10 layers, or even 1
layer and then add this at the end?

All your help is appreciated.

Regards