I dont know if same applies to Xp but in 98SE
create your logo in paint 110 x 110 pixels and save as Oemlogo.bmp you can then replace this in the system folder of windows by replacing the one that is already there if it is present. Note because of the size the logo you create should be very basic with few colours.
You can also replace Oeminfo with your own text by doing the same i.e create in note pad and replace in the sytem folder.
As I said this works in 98SE I do not know about XP as I have not done this in XP
If you go to Control panel/system your new logo and info should be there.
As a precaution save the existing files to disk in case you get things wrong and you can put them back to the original.