What else is running. I wouldn't want to run it like that but if the rest of your system is very very lean you could probably get away with it. The 4890 can draw upwards of 180W by itself. If you have a 65W CPU and 1 HD and 1 optical, you might be ok.
If it's as old as the Pent D, scrap the PSU and get a new one. I doubt the CPU will keep up with the 4890, so he needs to be looking at upgrading the whole system down the road. Find out what he wants to build, then get a 80+ PSU that can power the new system. If he wants to get another year+ out of that current system, keep the PSU but get a lesser vid card. A 4670 or so would probably be matched reasonably close to a Pentium D chip and would not tax the PSU.