However, you are going to run into continual problems for many reasons, half of them Santa Clara's MySQL Team's fault, the other half Redmond Microsoft Team's fault.
Some of the things you want to do [because you keep uninstalling and reinstalling with no progress]:
A.) Note Well! Once you assign the role of domain controller to Windows Server 2003, Data Execution Prevention [DEP] denies the launch and execution of all programs other than Microsoft programs. Therefore, things such as your motherboard drivers, nVidia, for example, which depends on an Apache for the GUI and Administrator's interface, will now no longer work after the role assignment of Domain Controller. You will also note that Distributed Component Object Model [DCOM] has been implemented upon role assignment, along with COM. These will absolutely prevent launch and execution on a per object basis, that is, in a refined set of not only programs, but the objects that are called by those programs. Thus, even if something like Network Access Manager [NAM], which is the nVidia Firewall and drivers installed as motherboard driver components, tries to launch and/or execute, it will be prevented by the object modelling and the DEP.
B.) You will note that, in general, installs to Windows Server 2003 systems using the standard msi will misplace the MySQL Service in all ControlSet's. Thus, you will find the the service with a bad name is under HKEY_LOCAL_MACHINE\SYSTEM\CurrentControlSet\Services instead of where it belongs
and in the outer block of the service containger [first key name] the name of the service will be wrong and will be MySQL Ser as a String (ab) Description.
C.) There will be no proper service for MySQL under the second key, which will not even exist.
The command, from a DOS prompt, to install the service is similar to:
"E:\MySQL5\bin\mysqld-nt.exe" --install MySQL5
if that matches your path. Using white spaces in directory names eventually will break something; installing to the standard Windows "C:\Program Files\MySQL Server 5.0\" is both rather lazy and will eventually break something. The suggested path would be better on a drive not the same as your operating system and something simple, like "E:\MySQL5" or similar.
This way, you can remove the entirety, as long as you also clean the Registry too.
Regardless of how you back up MySQL, once you uninstall MySQL completely, there does not appear to be a way to recover it, regardless of the protests of the MySQL Team, because if done properly the password is hashed [encrytped] and you cannot duplicate that encryption on a new install, hence, the saved database is useless and you've already lost the data. Even a simple MD5 hash will not repeat upon reinstall; recovering the data is nearly impossible, and the number of possible catastrophic losses due to corrupted passwords, even within the databases themselves, exponentially increases with each security dimension applied. That is, with the MySQL hash, followed by DEP, followed by DCOM, the number of possible lockouts has increased 2^3 and not just three times. Adding even more security features eventually leads to a point where recovery cost becomes impossible to justify as it eats up profit exponentially as well.
Oftentimes, the install of things such as phpMyAdmin and MySQLAdministrator link to sublayers of MySQL password protection and a reinstall of MySQL will be blocked by both of them, or, you will have to reinstall them as well and hope that you can connect them to the MySQL databases; often this too becomes impossible requiring a base zero reinstall of everything, hence, total loss of all data, again.
In fact, the subsequent install of any program that interacts with MySQL has the potential to destroy the connectivity, functionality, and integrity of databases; as has often been seen in the field, even if protested that is has not been seen in the MySQL Team test environments.
The prime example is the promotion of a Windows 2003 Server to the role of Domain Controller. But Apache for the nVidia motherboards stopped by the role is a second prime example. After that, any MySQL or PHP using program has the great potential to lock you out and result in a useless database, as well as a combined Apache, PHP, MySQL, Perl, and SSl installation. All of this magnificent security is compromised when MySQL fails and one is told to then set the root password to nil, leaving the server wide open to devastating attacks which have taken place and are well documented by such sites as guitarworld and MySpace.com
In all of this, the Santa Clara Team has chosen to completely ignore their single greatest problem: the Login Problem.
They keep saying it's not a bug; look at this: http://www.musics.com/manhtml/MySQL/MySQL5.howto.install.run.service.html
Something in there, or here: http://www.musics.com/manhtml/MySQL/mysql-host-denied-fix.type.html
should fix your problem, but there is not yet a reference to getting your database back because I have not been able to retrieve a MySQL database yet and don't know if it's possible.