Upgrading WinNT to Win2003

My company is currently considering upgrading our NT domain to Win2003. A little background info.: 1-NT PDC, 2-NT BDC’s, 1-NT File Server and the usual assortment of Win 3.11, Win95/98, Win2k, WinXP Pro machines. As the only IT guy for my company, I am considering a parallel install to make things as seamless as possible. My main question is, can I plug a Win2003 domain server into the same network as my NT domain thus having an NT domain and Active Directory domain on the same wire? Any suggestions on this or other ways to upgrade are greatly appreciated.

Thanks,

Mongooch