For Win Vista/7: Prepare your own OEM logo or image, cut / crop /shrink it to 120×120 pixels and save it as a Bitmap file.
Copy the BMP file to %windir%\system32 folder as OEMLogo.bmp.
1)Press Win+R to bring up the Run box.
2)type in %windir%\system32 and press enter.
3)copy the BMP file to the system32 directory and rename it to OEMLogo.bmp.
Next, open up Registry Editor.
1)Press Win+R to bring up the Run box.
2)Type regedit and press enter.
Browse to this Registry path:
HKEY_LOCAL_MACHINE\SOFTWARE\Microsoft\Windows\CurrentVersion\OEMInformation
(If you can’t find the OEMInformation key, right-click the CurrentVersion key, select New followed by Key option and name the new Key OEMInformation)
While at the OEMInformation key, right-click on the right-pane, select New followed by String Value:
Create the following keys:
1) Name of Key: Logo
Value of Key: the path to OEMLogo.bmp, i.e. C:\WINDOWS\system32\OEMLogo.bmp
2) Name of Key: Manufacturer
Value of Key: Whatever you want your manufacturer to be.
3) Name of Key: Model
Value of Key: Whatever you want your computer model to be.
The following keys are optional.
4) Name of Key: SupportUrl
Value of Key:
www.google.com 
5) Name of Key: SupportHours
value of Key: 24/7
6) Name of Key: SupportPhone
Value of Key: ...
If I have not been clear enough, here's an example of what the edit key box should look like.(I'm on XP so I can't browse to the actual directory I listed above.)
The finished result will be visible in the System Properties section.
_______________________________________
_______________________________________
For WinXP: Create a BMP file, but with dimensions 120x180 pixels. 120 pixels HIGH, 180 pixels WIDE.
1)Press Win+R to bring up the Run box.
2)type in %windir%\system32 and press enter.
3)copy the BMP file to the system32 directory and rename it to OEMLogo.bmp.
All WinXP needs is a simple oeminfo.ini file to display the logo and customized info.
Go to notepad, then paste this in:
----------------------------------------------------------
[General]
Manufacturer=We'll go with Apple.
Model=Mac Pro.
[Support Information]
Line1="This computer is manufactured by Apple through its"
Line2="1 infinite loop system and this Mac Pro is therefore prone to many"
Line3="device driver infinite loop BSODs. All Rights Reserved, Apple Inc."
Line4="Contact Steve Jobs at Apple.com"
-------------------------------------------------------------
You can create as many lines as you want in the similar format.
If you don't know how to save in .ini format, look at the sample picture below.
Save as type: All Files, File name: oeminfo.ini
_______________________________________
_______________________________________
__________
P.S.: I noticed this really funny description on MSI's website today.
This is sensible and is truly understanding. It is only 2 liters.
