I have tried building Python3a5 today using the tarball offered on your
internet site. 
The process './python -E setup.py build' keeps on allocating my memory
using more than 80% of my RAM, I am certain that it would have used more
if I had not cancelled it.
When I use ltrace to track the system calls and put it into the
Makefile, the resource usage still raises but much slower, if I use
ltrace and supply it a PID, the memory usage raises as fast as normal. I
think this is due to something in ltrace, it's understandable because it
produced a file of more than 600MB.

I attached an excerpt of the output of ltrace, showing you how the
system calls seem to repeat, and the output of './configure', 'make',
'uname -a', 'lspci' and 'lsmod' so you have some data about my system.
I also got a screenshot showing the output of htop, make and strace
together: http://img516.imageshack.us/img516/2275/screenshot1ab8.png.
Maybe the output of two different programs(ltrace and strace) will help
you too.
I tried out building the current SVN py3k branch, resulting in a similar
problem.
PS: It would help if you allowed uploading of multiple files to bug reports

Added the output of GDB as the memory usage was nearing 70%.
Hope it helps.

Turns out this is due to GCC 4.3 being used. Dupe of #2626.