tikitaha - I'm using Win2000 Pro Sp 4 and and I had to make an additional entry to the registry per Microsoft's instructions in order for Windows to see my 250GB drives.
Here is the article for Win XP:
From my understanding the XP SP1 or Win2000 sp3 or greater "allows" for 48bit lba support, but does not actually enable it. Only after i made the registry change did win2000 see my drives.
I'm not as familiar with XP though so Ste or someone please correct me if I'm wrong.