There are allot of different types of tablets, depending on your budget you can find decent tablets for drawing. The only thing I am thinking is, does he have any experience with tablets before?
Because it's not as simple as it looks. The home use tablets/ or should I say older versions of tablets did not have an integrated LCD display into the tablet which means you'll spend a lot of time glancing between the tablet and your computer display to get the image right.
These tablets you can get for lets say $100 to $250.
Though saying that, new and advanced tablets have built in LCD on to the tablet, so when you designing something it incorporates the image on the tablet so you don't have to switch constantly at tablet and screen. However they are quite expensive. For example their range could be from $1000 to $2000.
Here is the link of a company I think is quite good [http://www.wacom.com/cintiq/21UX.cfm]
So depending on what he is looking for and how much experience he has, how much budget you have for his tablet, I'd say you should then invest accordingly.
As far as gaming PC is concern, to be honest that depends on what type of games he plays. If he plays strategy games then I don't think he needs any mega powerful PC however if he plays like FPS(First person shooters) like Call of Duty 4, BioShock, FarCry2, Crysis etc then he needs a much bigger and better PC (that means to invest like $1000,$2000).
The reason is that you need to have a very good graphics card to run these types of games, additionally a big memory (say about 2GB), a bigger hard drive (Flight Simulator takes 15GB of space to install), a better sound card (Creative Audgiy 7.1).
Again it depends how much you want to spend on a gaming PC and what kind of games he plays.
Additionally Mac system games are very few and not many companies make them, though they do sell but not as much as PC. Maybe that is the reason he wants a PC?
So find it out and let us know and I will try to help you further