Sure many sharepoint Admin/ Developers/Architects must have come across this issue when trying to  uninstall and re- install Sharepoint 2007.
I have uninstalled sharepoint instance before just by going to the Add Remove programs and it was a breeze.
But on my Dev server when i tried the same but nothing basically happened. The status bar did show as if it was uninstalled but when i go back and check nothing was removed :(

I later found this which did help :www.howtonetworking.com/msapps/wss14.htm

Which stated different ways to uninstall it....
But after taking all the steps posted on that site above you have to remember to do one thing  STEP 7 in METHOD 2.
I actually did it but after running the sharepoint config wizard i get the error:

The language is not supported on the server

When i looked the the registry i couldn't find the entry so i added it manually and after that the error dissapeared.

But as the wizard was running to configure the Sharepoint_Config database another error popped up :(

MSSQLSERVER login failed for user 'MACHINE or DOMAIN\user'. [CLIENT: <local machine>]

This error is very common as i found scenarios were it wasnt only related to  Sharepoint but to other products like SQL Reporting services etc...


The main problem is that when you remove a DB or put it Offline that error basically starts every minute.
This happens because Sql Agent is responsible to 

Solution(not related to Sharepoint):
For those of you that have installed an ASP.net application or state server in SQL Server, you will have to use the aspnet_regsql tool to remove it.  Manually deleting the databases or taking them offline will produce these errors.

Here is one of them that doesn't relate to sharepoint and you can read more  here


Post and Solution related to  Sharepoint: here
Solution:
You need to go into sql server management studio and disable the job called SharedServices_DB_job_deleteExpiredSessions

Also see this post here

Hope this helps