Installing Windows 2003 DC in a Windows 2000 AD mixed domain with 1 NT 4.0 BDC still active

I have a Windows NT 4.0 Domain network with 1 PDC which is also running exchange  5.5 and  1 BDC, which bacically just serves as a BDC . I need to install a new windows 2003 server and upgrade to 2003 active dir domain.

I have promoted the BDC to be the PDC and setup the old PDC to be the BDC, so I and keep the exchange server off the PDC during the upgrade, I then installed WINDOW 2000 Server on the  PDC and installed AD in mixed mode, all appers operational, including access to the existing exchange 5.5 server which again is now on the BDC. I am aware that having the exchange on a domain controller is not a good idea, and I will address that a bit later, I did not originally setup this network.

The computer which now is the WIN2000 DC, I dont think is capable of running 2003, I was planning to setup a temp 2000 server, join to the domain, promote to a DC, then install the win2003 server on that.

I just have a few questions, I read several of the responses already listed here and I just need to cofirm.

I have a new dell Windows 2003 server as a member of the domain, not a dc, if I run DC Promo on this machine, can this be a dc in the 2000 domain running in mixed mode? If I run adprep first before promoting the DC, will this convert the 2000 ad to 2003?

Basically can I upgrade the 2000 ad to 2003 ad while promoting this 2003 member server or do I have to upgrade a 2000 machine to 2003 to upgrade the ad to 2003. What I understand from reading some of the responses here, that if I run dcpromo the 2003 unit, it will be a DC in the 200o domain, if I run ADprep first, then the domain will be upgraded to 2003, is that correct.

Later I plan on installing exchange 2003, on another member server, then do a swing migration over to this new exchange server, then retiring that last NT bdc and changing to native mode and I need to make sure that this exchange remains operational while I upgrade the domain.

thanks
Steve