problems installing ruby 1.9.1-p378 on snow leopard

Question

i've installed the latest upgrades to the dev tools, and tried re-installing, and yet i still get this error:

You have to install development tools first.
from /Users/jian/Downloads/ruby-1.9.1-p378/lib/mkmf.rb:427:in try_compile'
from /Users/jian/Downloads/ruby-1.9.1-p378/lib/mkmf.rb:473:intry_static_assert'
from /Users/jian/Downloads/ruby-1.9.1-p378/ext/bigdecimal/extconf.rb:5:in

When installing Ruby 1.9 with rvm, I get the following error:

[2010-05-19 22:06:38] make
main.c: In function ‘objcdummyfunction’:
main.c:19: warning: implicit declaration of function ‘objc_msgSend’
main.c: At top level:
main.c:19: warning: ‘objcdummyfunction’ defined but not used
eval.c: In function ‘ruby_cleanup’:
eval.c:139: warning: passing argument 1 of ‘ruby_init_stack’ discards qualifiers from pointer target type
gc.c: In function ‘garbage_collect_with_gvl’:
gc.c:597: warning: cast from pointer to integer of different size
ar: libruby-static.a: Invalid operation
make: * [libruby-static.a] Error 1

any help would be much appreciated.