ACR/PS Update needed - Help Please

I've been shooting a D60 for about 4 years now and using CS3 and ACR 4.5 for PP. Just bought a D5100 and have found that I can't open from Bridge into Camera Raw. A window in Ps says that the file type is unsupported. An excursion to the Adobe site to update ACR (6.4.1.?) to D5100 wouldn't work. Does this mean that CS3 is too old to support the update and, if so does that mean that I have to buy into CS5 etc?

I'd be very grateful to hear from someone who knows about this.

Thanks in Advance,

Kevin