Hello,
MCU functionality has been added for only 2 PICs, and Intel based controllers, as well as some RAM and ROM, but ATmega controllers are not.
Microcontrollers (IMO) are incredibly complex and would be very hard to program their entire functionality on SPICE and thus we don't see a lot of them. I've looked around the web trying to see if anyone had made a spice model for AVRs but I wasn't able to find any. My recommendation is if you need this for prototyping, get the board, If you just need this for a PCB and already know what to expect then create an atmega32 footprint in multisim (a dummy model) so you can create a circuit pretending the board is there.
Kind Regards,
Miguel V
National Instruments