Not really sure what good a cheap Yamaha/Roland/Whatever is going to do if he just wants a computer interface. Most controllers do USB and MIDI, simple setup and will sync with popular programs. Not to say the cheaper Keyboards won't, but there is no need to use a keyboard with samples/speakers/etc as a controller if a better supported controller will do the same job for the same price.
Also, it sounds like he is heading into Reason territory, or at least acid. If I am guessing correctly, he isn't looking for a composition program like sibellius. That program is basicly for writing and printing sheet music anyway. CakeWalk is probably overkill for this type of thing as well.
Honestly, Reason kicks so much ass, but it will kick your ass as well, steep learning curve, but very rewarding. There are a lot of sample based applications that you can set a decent keyboard up to interface perfectly (all nobs, pads, sliders, etc work... not to mention after touch, etc).
There is nothing wrong with going the cheap keyboard route, but if it is going to be used primarily with a computer or synths... then I still say a controller is probably a better bet...
-Nick