For Pro-Tools your going to need the hardware. For instance, Pro Tools M-Powered is a more affordable way to get started with the software. And then, Pro Tools LE w/ an Mbox/Digi is another route. More serious, Pro Tools HD. So since you are starting out, unless you have the money and are serious, Pro Tools is a big investment and if you have no prior experience, can be difficult to learn. If you are serious however, it's worth it, as Pro Tools is still the standard.
I recommend you get a solid audio interface and Cubase SX. If you run MAC, get Logic.
You'll also need a studio condenser microphone, there are plenty budget mics out there, very affordable. I'd also invest in a good pre amp if your just doing vocals over beats.
There are many ways to go about it, research. I wouldn't recommend you go and break bread on a bunch of equipment and software just because your friend is good at rapping, unless your serious about music yourself, which it seems to me your just getting into it and have no idea where to start.
Your friend needs studio time, if he's serious, he should know that. He can book himself studio time.