I just updated an Ubuntu 10.04 kernel to 2.6.32-27-generic, and a wifi driver (r8187) is not present there.
Is the only solution reinstalling it or is there a simple way to move it from an older kernel I have on the same machine?
That driver is probably not in the kernel tree. You can't just copy driver modules from one to the other. Each driver has to be built for that exact kernel. There is probably another package that contains that driver that you also have to install after upgrading your kernel.