My buddy just bought a 500 GB external esata 2 hard drive and it has usb a2.0 or esata but it won't recognize in XP.

I thought he needed a 2.5 external but I've read that people can use the 3.5 without the adapter he leaves for Iraq in a few days and I wanted to fix it for him before he goes.

Does he need a new 2.5 or can he get the existing 3.5 to work?