I absolutely wouldn't suggest anyone use a 10 year old PSU under any circumstances. Not even if it sat in a box for that whole time.
What PCs pull from each voltage type has changed completely in that time, making 10 year old PSUs provide power pretty much opposite of how people need it now.
I would definitely tell him to get a new PSU from Antec, Corsair, Seasonic, or XFX only. No other makers will do.
The hard drive from the old PC will probably be standard ATA which uses a ribbon cable and it may take considerable effort to find a motherboard that will support this. You could end up putting it on the same ribbon cable as the CD drive which would hurt performance.
I would instead just buy a whole new SATA hard drive as well. Your 10 year old hard drive will probably only hold like 10 or 20 GBs worth of data, guesstimating, which probably means you will be able to get an OS on it and like one game and that is all. Just get a cheapy 250 GB or something instead of this.
The case is probably fine, but it will not have optimal cooling which means the parts will wear down faster, especially the PSU. Cases 10 years ago pretty universally used top mount PSUs which takes all the heat out of the case and sucks it into the PSU before blowing it out the back.
That greatly reduces PSU longevity in general.
Such cases were built for a time when heat output was 90% less than it is now, so while it may have been good enough in the past it may not be good enough now. There may also not be room for such important things as side fans and rear fans to assist in keeping parts cool and sucking heat out of the case.
Really, I would just not use any of those parts.
You can get a reasonable gaming PC on the low end for under $300 and it will just work so much better and last so much longer if you can go that high than if you try to use the older parts.