I plan to build a new PC with Ivy Bridge i7-3770k, and I may reuse a P150 that I already have.
Is it possible to upgrade the front USB ports of the P150 to USB3?
I looked on Antec's website, but they don't seem to have any USB3 upgrade kit.

There are several front panel devices that fit in a 3.5" or 5.25" external drive bay that have USB3. I would assume this would be satisfactory? You can search NewEgg with "usb3 front panel"

If you want the case's USBs to be USB3, I've now idea if it would definitely work but, you might be able to get a adapter kit that plugs in to the motherboard and splice the wires in to the P150s front USB wires.
I think it should work as you can get various USB 3 to 2 adapters, might even be able to get the "right" one.
Seb

@m0002a: I haven't thought of a 5.25" bay adapter, thank you for the suggestion, this would do too.

@SebRad: I would have preferred to have the case USBs to be USB3, but if there's no guaranteed USB3 kit,
then I won't tinker and risk damage to the new build.