Hard to say here. Officially the Intel site claims that the GL960 should only support Celerons, but there's quite a few reports of people using C2D on a GL960, so I'm not really sure of the best way to go around this one...
Barring chipset limitations, you're mechanically good through a T7800 since it's Socket P; a T5500 will definitely not work since that's Socket M.
So my point is it is hard to say what processors are compatible because of the discrepancy between official and practical limitations; I'm not sure of ALL GL960 chipsets will actually support a 667MHz or even 800MHz FSB or just a few special ones that might be like downgraded GM965 chips.
Ah well I have an HP Compaq 6720s with a Celeron M 540 and wanted to upgrade to a T7100 I won on eBay for an amazing £41! Unfortunately I've found out that the chipset is the GL960 (I assumed that the laptop was using GM965). I don't know if the laptop would recognize the T7100 at all, it might run at 533 FSB instead of 800MHz (if that's possible) but probably won't work at all. I could always attempt it but I have to disassemble my laptop and if there are no guarantees then is there a point?
This confirms GL960 and 667MHz Core 2 Duos are compatible: