I expect it'll be okay, especially if you're using windows 2000 or xp; they multitask badly, but much much better than 95/98/me.
Bear in mind the main issue with CPU speed is "can it feed the burner fast enough?". So if you should experience problems, you can almost certainly choose a slower burn speed to get by.
A very important point: when you first install a drive, the system will usually mark it for PIO operation. Make a point of checking, and setting the interface to "use DMA if available" and reboot. It will make a huge difference.