Why isnt my GPO being run ?

I have just converted from an NT 4 domain to Win 2k with active directory. I have created an OU called Finance and under that OU’s called Computers and Users. My test user and 2 test computers reside in the relevant OU. At the Finance level i’ve created a GPO. If i log onto the 2 PCs, with the same user id, the GPO is applied to one and not the other? Both are running Win2k SP2 – the only differance is one was built while the domain was NT4 and the other built after conversion. I’ve trieddeleting the computer account and rejoining the domain.