Confused about 64bit

[Graham Smith <graham@crazysquirrel.com>]

Hi, I'm confused and I hope that you can help me out.

I'm running the pure64 port of Debian on an AMD64.

My understanding about the AMD64 was that is could run in three modes:

1)32 bit emulation mode where you are using a 32bit kernel and 32 bit 
libraries (eg WinXP).
2)mixed mode with a 64 bit kernel and 32 bit libraries (eg "Normal" 
Debian with 64 bit kernel)
3)full 64 bit mode (64bit Debian port)

I thought that in full 64 bit mode it was impossible to run 32 bit 
applications unless the 32 bit libraries had been tweaked to allow it. 
But, and here's the strange bit, I am running the 32 bit Sun Java VM 
under the 64 bit environment quite happily without the ia32-libs package 
installed. How come this works? Surely the VM is compiled against 32 bit 
libraries and therefore shouldn't work when running against the 64 bit 
ones? That of course then raises the question why don't other 32 bit 
applications like OO work under 64 bit?

I suspect there is a hole in my knowledge but I don't know where. A 
quick lesson would be appreciated. Many thanks,

Graham