Need more than 4GB of ram? - do it compile your debian kernel
If you need support for more than 4GB of ram in your kernel, then you have to compile your own kernel, or get someone else to do it for you.
Googling i found about linux memory model (described in kerneltrap.org)
UPDATE :i installed kernel 2.6.10 and it have support for big MEMORY the only drawback is : there is no sound on my box now ... Oh well going back to 2.6.9