Hey there Richard, First I would like to say that bootscreens are pretty touchy, system wise, and I have had my own personal trials with them..Be careful, otherwise you may find yourself asking a whole bunch more questions upon recovering from a MAJOR bootscreen disaster..LoL
I also have never created one, but I do know there is certain criteria they have to meet, it may just be that you havent met all of the necessary criteria.
As far as I understand them to be, the bootscreen has to be created as..
1.A BMP file
2.640x480
3.4bit 16 color Data type
Im sure all of these things have got to be true for windows XP for your screen to work, if there are any other criteria, I am not aware of them..Hopefully one of the more experienced authors will jump in and tell us..
Anyway, check your file and be sure it meets all of those perameters..it's at least something to work with..Sorry I couldnt be of more help.
Good Luck,
Zero.