Moving Servers with Public IPs to Private Network

I have 2 servers one Win2K SP4 and the other 2003 R2.  Each is a DC with AD for its own domain. Each is running DNS and has a public IP provided by the ISP.  The configuration looks like:

Router1 ------ xxx.xxx.xxx.193  (provided by ISP)
   |
   |
server-1 xxx.xxx.xxx.194 (Domain1.com www, e-mail, ftp)
server-2 xxx.xxx.xxx.200 (Domain2.com www, e-mail, ftp)
Router2 xxx.xxx.xxx.205 (NAT, DHCP)
   |
   |
Clients for Domains 1 & 2 (192.168.1.xxx)

I am not running a firewall and have just purchased a PIX 501. I want to replace Router2 with the PIX and relocate the servers to the internal side.  I am comfortable with the IP issues related but I am not as comfortable with any Active Directory problems that changing a DCs IP may have.  Is it safe to change the IP address of an Active Directory Domain Controller?

Thanks,
DRBibens