AVR-Chat

I am trying to port some code over from a Motorola HC08 project
compiled with Cosmic's C compiler to an AVR Mega.  One of the
functions that I use is vsprintf but it doesn't seem to be included in
the WinAvr package (gcc v3.3.1 ?) although it is mentioned in the
documentation.  

Anyone know if this function is available in avr-gcc?

Thanks.