help me! mod rewrite script subdomain alias

[prynut]

i need chang script

[mydomain.com...]
to
[mydomain.com...]

[mydomain.com...]
to
[mydomain.com...]

and chang *.php to .html by rewrite

and i need to create subdomain alias

exsample :
[mydomain.com...]

to ..

[baby.mydomain.com...]

help me
thank