Are there any advantages or disadvantages to installing a 64-bit linux distro, such as SuSE SLES 10 or RHEL 4/5 on 32-bit hardware?

I believe that the 32-bit distro will install run-time libraries and kernel that will limit the maximum process size to 2^32 bytes, and kernel maximum addressable memory to 4GB.

Similarly, the 64-bit distro will install run-time libraries and a kernel that increases the maximum process size to 2^64 bytes and 4 exabytes (2^64) of memory.

I'm not sure about the accuracy of the last statement, and that's why I'm here ;-)

I know that the 64-bit kernel, along with a processor with PAE support will allow the kernel to address more than 4GB of memory, but not sure if the installation of the 64-bit run-time libraries on 32-bit hardware will allow a 64-bit executable to access more than the default 2^32 address space of the processor.

Any discussions, corrections or clarifications are appreciated.

You cannot run 64bit on a 32bit cpu. You can run 32bit(or 64bit) on a 64bit cpu.

The reason a 32-bit processor can only address 4GB is because there are physically only 32-bits. Presuming that you have an x86_64 machine, the 64-bit instruction set is larger than the 32-bit instruction set. A 32-bit processor will not have the slightest idea what to do if it gets one of those instructions. The x86_64 architecture also has additional registers and the registers are wider (2 times in fact) that those in x86 processors. Depending on the 64-bit architecture you have a 64-bit processor may run 32-bit as well as 64-bit, but not all are multilib.

To answer your question, the disadvantage of installing a 64-bit distro on a 32-bit machine is that the machine won't work. The advantage is that you can use it as a doorstop.

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s/processor/process/
Using PAE the (32-bit) processor can address 64 Gig (real).

No argument with the rest.