there is a lot of confusion in this thread, due mainly to the broken English.
from what i can see, the original post was meant to say that:
1. They have successfully managed to get a PC bootable installation of Windows XP on a microSD card, and by using the N900 as a microSD card reader, using the mentioned card to boot up their PC from the N900
2. The original poster would prefer to have Windows 7 on the microSD card, but after formatting the card (i would assume with Windows on a PC, via the N900 acting as a card reader) the N900 cannot see the microSD card anymore, and is asking for assistance.
i would suggest that Windows 7 will give you a headache here, since it seems that you need underlying system support in maemo so that the N900 can recognise the NTFS formatted microSD card.