I knew this would turn into what it has become.
I use macs, but I see the relevance of PCs. And PCs are great for gaming, much better than the mac.
Keep in mind, that I was a sales associate, inventory specialist, and a middle manager for a west coast Apple Retail Store. When my MANAGER conviced me to grab a P4 with all the fixins, I was in gamng nirvana. AOM, WC3, BF1942 - all of them. I wish I still had it so that I could play HL2, UT2K4, and all the other goodies that are due out soon.
And I've done comparisons between the 2 systems. I've played an extensive amount of WC3 on a mac dual G5 2gig and my sorely missed P4 3.22 (or somewhere around there), and there is no comparison between the two: the PC version is smooth as hell. I'll choose the mac for it's user interface any day, but the PC get's my vehement support when it comes to gaming and graphical prowess.
Just take it for what it's worth. That's a comment in regards to both macs and PCs. And don't try to convice PC users otherwise - who cares if they don't like macs? I'm an Apple zealot myself, but I can understand if something other than a mac works better for them in the things that they do.
Back on subject...
As far as games for your brother's iBook, go with the standards. WC3, AOM, The SIMS, Diablo...
Also Baldur's Gate 2, Fallout 2, Tropico, Wingnuts (kind of like Time Pilot, suprisingly fun), etc. These ones I mentioned here go for about $20 a pop.
Now I'm not sure of how efficiently the G4 chips in iBooks run, but when it was a G3, there was definately a performance disparity (compared to a G4). Also keep in mind of what the graphics card is capable of. I haven't kept up with Apple hardware ever since I left Apple Retail, so you'll have to do your own footwork. Some games I would not even attempt to play on a laptop, mainly FPSs. Hell, I just finished Dungeon Siege on a 1ghz G4 powerbook with 1.25 gigs of DDR RAM, and a pretty solid mobile graphics card, and it STILL had major slowdown. So go by basic rules of thumb - the more graphically complex it is, the less likely you'll get acceptable performance on a laptop. That's what desktops are for.
And don't discount the shareware games out there for mac, they're pretty awesome in their own right. Enigmo, Big Money, Bejeweled, etc. Check out
www.popcap.com, or go to
www.versiontracker.com for sharewares.
Come on kids. Let's all be friends.